diff --git a/src/js/account.js b/src/js/account.js
index 73f0eff..9ccd65b 100644
--- a/src/js/account.js
+++ b/src/js/account.js
@@ -5,13 +5,18 @@ class Account {
         this.keypair_ = keypair;
         this.id_ = id;
         this.amount_ = 0;
-        if (!this.keypair_) { }
-        if (!this.id_) { }
+        if (!this.keypair_) {
+            // load from file
+        }
+        if (!this.id_) {
+            // load from file
+        }
     }
 
     get_id() { return this.id_; }
     get_key() { return this.keypair_; }
     get_amount() { return this.amount_; }
+    set_amount(amount) {this.amount_ = amount;}
 }
 
 module.exports = Account;
\ No newline at end of file
diff --git a/src/js/block.js b/src/js/block.js
index c962736..593c470 100644
--- a/src/js/block.js
+++ b/src/js/block.js
@@ -1,14 +1,14 @@
 'use strict';
 
 var EventEmitter = require('events').EventEmitter;
-var crypto = require("crypto");
-var ed = require("ed25519");
+var Crypto = require("./crypto");
+
 
 class Block extends EventEmitter {
     constructor(data, consensus) {
         super();
         // body
-        this.transcations_ = data ? data.transactions : [];
+        this.transactions_ = data ? data.transactions : [];
         // header
         this.version_ = 0;
         this.height_ = data ? data.previous_block.height + 1 : -1;
@@ -37,7 +37,7 @@ class Block extends EventEmitter {
     get_timestamp() { return this.timestamp_; }
     get_signature() { return this.block_signature_; }
     get_publickey() { return this.generator_publickey_; }
-    get_transcations() { return this.transcations_; }
+    get_transactions() { return this.transactions_; }
     get_consensus_data() { return this.consensus_data_; }
     set_consensus_data(data) { this.consensus_data_ = data; }
     toObject() {
@@ -51,7 +51,7 @@ class Block extends EventEmitter {
             "hash": this.hash_,
             "block_signature": this.block_signature_,
             "consensus_data": this.consensus_data_,
-            "transcations": this.transcations_
+            "transactions": this.transactions_
         };
         return block;
     }
@@ -65,23 +65,20 @@ class Block extends EventEmitter {
         this.hash_ = data.hash;
         this.block_signature_ = data.block_signature;
         this.consensus_data_ = data.consensus_data;
-        this.transcations_ = data.transactions;
+        this.transactions_ = data.transactions;
     }
 
-    calc_hash(data) {
-        return crypto.createHash('sha256').update(data).digest('hex');
-    }
     calc_merkle_hash() {
-        // calc merkle root hash according to the transcations in the block
+        // calc merkle root hash according to the transactions in the block
         var hashes = [];
-        for (var i = 0; i < this.transcations_.length; ++i) {
-            hashes.push(this.calc_hash(this.transcations_.toString('utf-8')));
+        for (var i = 0; i < this.transactions_.length; ++i) {
+            hashes.push(Crypto.calc_hash(this.transactions_.toString('utf-8')));
         }
         while (hashes.length > 1) {
             var tmp = [];
             for (var i = 0; i < hashes.length / 2; ++i) {
                 let data = hashes[i * 2] + hashes[i * 2 + 1];
-                tmp.push(this.calc_hash(data));
+                tmp.push(Crypto.calc_hash(data));
             }
             if (hashes.length % 2 === 1) {
                 tmp.push(hashes[hashes.length - 1]);
@@ -93,8 +90,8 @@ class Block extends EventEmitter {
 
     prepare_data() {
         let tx = "";
-        for (var i = 0; i < this.transcations_.length; ++i) {
-            tx += this.transcations_[i].toString('utf-8');
+        for (var i = 0; i < this.transactions_.length; ++i) {
+            tx += this.transactions_[i].toString('utf-8');
         }
         let data = this.version_.toString()
             + this.height_.toString()
@@ -109,11 +106,11 @@ class Block extends EventEmitter {
     }
     // calc the hash of the block
     calc_block_hash() {
-        return this.calc_hash(this.prepare_data());
+        return Crypto.calc_hash(this.prepare_data());
     }
     sign(keypair) {
         var hash = this.calc_block_hash();
-        return ed.Sign(Buffer.from(hash, 'utf-8'), keypair).toString('hex');
+        return Crypto.sign(keypair, hash);
     }
     make_proof(consensus, keypair) {
         let self = this;
@@ -128,13 +125,7 @@ class Block extends EventEmitter {
 
     static verify_signature(block) {
         var hash = block.hash;
-        var res = ed.Verify(Buffer.from(hash, 'utf8'), Buffer.from(block.block_signature, 'hex'), Buffer.from(block.generator_publickey, 'hex'));
-        return res;
-
-    }
-
-    static get_address_by_publickey(publicKey) {
-
+        return Crypto.verify_signature(hash, block.block_signature, block.generator_publickey);
     }
 
 }
diff --git a/src/js/blockchain.js b/src/js/blockchain.js
index 222a748..6886ce2 100644
--- a/src/js/blockchain.js
+++ b/src/js/blockchain.js
@@ -4,17 +4,22 @@ var Block = require("./block");
 const genesis_block = require("./genesis_block.json");
 var Node = require("./network");
 var Account = require("./account");
-var Transaction = require("./transaction");
+var Transaction = require("./transaction").Transaction;
+var TxInput = require("./transaction").TxInput;
+var TxOutput = require("./transaction").TxOutput;
 var Msg = require("./message");
 var MessageType = require("./message").type;
 var Promise = require("bluebird");
+var level = require("level");
+var Crypto = require("./crypto");
 
 var Pbft = require("./consensus/pbft");
-let pbft = true;
+let pbft = false;
 class BlockChain {
     constructor(Consensus, keypair, id, is_bad = false) {
         // todo
         this.pending_block_ = {};
+        this.tx_pool = {};
         this.chain_ = [];
 
         this.is_bad_ = is_bad;
@@ -22,14 +27,26 @@ class BlockChain {
 
         // ///////////////////////////////////////
         this.genesis_block_ = genesis_block;
-        this.last_block_ = genesis_block;
-        this.save_last_block();
+
 
         this.account_ = new Account(keypair, id);
         this.consensus_ = new Consensus(this);
         this.node_ = null;
     }
-    start() {
+    async start() {
+        this.db_ = level(`/tmp/data_${this.get_account_id()}`);
+        try {
+            // load blocks
+            let last = await this.db_.get("last_block");
+            this.last_block_ = JSON.parse(last);
+            console.log(`node: ${this.get_account_id()} last block: ${this.last_block_.height}`);
+        } catch (err) {
+            // empty chain
+            this.last_block_ = genesis_block;
+            this.save_last_block();
+            console.log(`node: ${this.get_account_id()} empty`);
+        }
+
         this.node_ = new Node(this.get_account_id());
         this.node_.on("message", this.on_data.bind(this));
         this.node_.start();
@@ -57,18 +74,40 @@ class BlockChain {
         cb();
     }
 
-    save_last_block() {
+    async save_last_block() {
         // query from db via hash
         // if not exist, write into db, else do nothing
-        // todo（tx is also need to store?）
         if (this.pending_block_[this.last_block_.hash]) {
             delete this.pending_block_[this.last_block_.hash];
         }
-        this.chain_.push(this.last_block_);
+        await this.db_.put(this.last_block_.hash, JSON.stringify(this.last_block_));
+        await this.db_.put("last_block", JSON.stringify(this.last_block_));
+        // console.log(`save block: ${this.last_block_.hash} to db`);
+
+        // tx
+        if (!this.last_block_.transactions) {
+            return;
+        }
+        for (var i = 0; i < this.last_block_.transactions.length; ++i) {
+            let tx = this.last_block_.transactions[i];
+            if (this.tx_pool[tx.id]) {
+                delete this.tx_pool[tx.id];
+                // console.log(`node ${this.get_account_id()} delete tx ${tx.id}`);
+            }
+            await this.db_.put(tx.id, JSON.stringify(tx));
+        }
     }
     generate_block(keypair, cb) {
-        // load transcations
-        var tx = [];
+        // load transactions
+        var tx = [this.create_coinbase()];
+        var i = 0;
+        for (let key in this.tx_pool) {
+            if (i == 10)
+                break;
+            tx.push(this.tx_pool[key]);
+            i++;
+            console.log(`node ${this.get_account_id()} load tx ${key}`);
+        }
         // create block
         let block = new Block({
             "keypair": keypair,
@@ -79,7 +118,7 @@ class BlockChain {
         let self = this;
         block.on('block completed', (data) => {
             if (data.height == self.last_block_.height + 1) {
-                console.log("block completed");
+                // console.log("block completed");
                 self.commit_block(data);
 
                 self.broadcast(Msg.block(data));
@@ -113,15 +152,32 @@ class BlockChain {
     get_height() {
         return this.last_block_.height;
     }
-    get_block(hash) {
+    async get_from_db(hash) {
         // query block with hash value
-        // todo
-        for (var i = 0; i < this.chain_.length; ++i) {
-            if (this.chain_[i] == hash) {
-                return this.chain_[i];
-            }
+        try {
+            let block_data = await this.db_.get(hash);
+            let block = JSON.parse(block_data);
+            return block;
+        } catch (err) {
+            return null;
         }
-        return null;
+    }
+    async iterator_back(cb, hash) {
+        if (!hash) {
+            return;
+        }
+        let block = await this.get_from_db(hash);
+        let res = cb(block);
+        if (res)
+            await this.iterator_back(cb, block.previous_hash);
+    }
+    async iterator_forward(cb, hash) {
+        if (!hash) {
+            return;
+        }
+        let block = await this.get_from_db(hash);
+        await this.iterator_forward(cb, block.previous_hash);
+        cb(block);
     }
     get_last_block() {
         return this.last_block_;
@@ -140,41 +196,89 @@ class BlockChain {
     get_account_keypair() {
         return this.account_.get_key();
     }
+    get_public_key() {
+        return this.get_account_keypair().publicKey.toString('hex');
+    }
     broadcast(data) {
         this.node_.broadcast(data);
     }
     list_peers() {
         return this.node_.list_peers();
     }
+    async verify_transaction(tx) {
+        let input_amount = 0;
+        for (var i = 0; i < tx.input.length; ++i) {
+            let input = tx.input[i];
+            // coinbase
+            if (input.id == null) {
+                // todo check milestone
+                if (tx.output[0].amount == 50) {
+                    return true;
+                } else {
+                    return false;
+                }
+            }
+            let vout = null;
+            if (this.tx_pool[input.id]) {
+                vout = this.tx.tx_pool[input.id];
+            } else {
+                vout = await this.get_from_db(input.id);
+            }
+            if (!vout) {
+                // invalid vout
+                return false;
+            }
+            vout = vout.output[input.index];
+            let res = Crypto.verify_signature(JSON.stringify(vout), input.ScriptSig, vout.ScriptPubKey);
+            if (!res) {
+                return false;
+            }
+            input_amount += vout.amount;
+        }
+        let output_amount = 0;
+        for (i = 0; i < tx.output.length; ++i) {
+            output_amount += tx.output[i].amount;
+        }
+        if (input_amount < output_amount) {
+            return false;
+        }
+        return true;
+    }
     // verify the block is valid
-    verify(block) {
+    async verify(block) {
         // verify the block signature
         if (!Block.verify_signature(block))
             return false;
         // verify consensus
         if (!this.consensus_.verify(block))
             return false;
-        // verify transcations
-        let tx = block.transcations;
-        for (var i = 0; i < tx.length; ++i) {
-            // todo (check tx is exist and valid)
-            if (!Transaction.verify(tx[i]))
-                return false;
+        // verify transactions
+        let tx = block.transactions;
+        if (tx) {
+            for (var i = 0; i < tx.length; ++i) {
+                if (!await this.verify_transaction(tx[i]))
+                    return false;
+            }
         }
         return true;
     }
-    on_data(msg) {
+    async on_data(msg) {
         switch (msg.type) {
             case MessageType.Block:
                 {
                     let block = msg.data;
                     // console.log(`node: ${this.get_account_id()} receive block: height ${block.height}`);
                     // check if exist
-                    if (this.pending_block_[block.hash] || this.get_block(block.hash))
+                    let query = await this.get_from_db(block.hash);
+                    if (this.pending_block_[block.hash] || query) {
+                        // console.log("block already exists");
                         return;
+                    }
                     // verify
-                    if (!this.verify(block))
+                    if (!await this.verify(block)) {
+                        // console.log("verify failed");
                         return;
+                    }
 
                     this.pending_block_[block.hash] = block;
 
@@ -195,6 +299,22 @@ class BlockChain {
             case MessageType.Transaction:
                 {
                     // check if exist(pending or in chain) verify, store(into pending) and broadcast
+                    let tx = msg.data;
+                    if (this.tx_pool[tx.id]) {
+                        // already exists
+                        return;
+                    }
+                    this.tx_pool[tx.id] = tx;
+                    // verify transaction
+                    let res = await this.verify_transaction(tx);
+                    if (!res) {
+                        delete this.tx_pool[tx.id];
+                    } else {
+                        // console.log(`node ${this.get_account_id()} store tx ${tx.id}`);
+                    }
+
+                    // broadcast
+                    this.broadcast(msg);
                 }
                 break;
             default:
@@ -218,7 +338,7 @@ class BlockChain {
     }
     async fork() {
         console.log('----------fork----------');
-        // load transcations
+        // load transactions
         var tx1 = [{
             amount: 1000,
             recipient: 'bob',
@@ -242,7 +362,7 @@ class BlockChain {
             });
         });
 
-        // load transcations
+        // load transactions
         var tx2 = [{
             amount: 1000,
             recipient: 'cracker',
@@ -279,6 +399,91 @@ class BlockChain {
         console.log("fork");
         this.commit_block(block_data1);
     }
+    create_coinbase() {
+        let input = new TxInput(null, -1, `${new Date()} node: ${this.get_account_id()} coinbase tx`);
+        let output = new TxOutput(50, this.get_public_key());
+        let tx = new Transaction([input], [output]);
+        return tx;
+    }
+
+    async get_utxo(cb) {
+        let publicKey = this.get_public_key();
+        let spentTXOs = {};
+        await this.iterator_back((block) => {
+            let txs = block.transactions;
+            // tx
+            for (var i = 0; i < txs.length; ++i) {
+                let tx = txs[i];
+                let transaction_id = tx.id;
+                // output
+                for (var j = 0; j < tx.output.length; ++j) {
+                    let output = tx.output[j];
+                    // owns
+                    if (output.ScriptPubKey == publicKey) {
+                        // not spent
+                        if (spentTXOs.hasOwnProperty(transaction_id) &&
+                            spentTXOs[transaction_id].hasOwnProperty(j)) {
+                            continue;
+                        } else {
+                            if (!cb(transaction_id, j, output)) return false;
+                        }
+                    }
+                }
+                // input
+                for (j = 0; j < tx.input.length; ++j) {
+                    let input = tx.input[j];
+                    // not coinbase
+                    if (input.id != null && input.index != -1) {
+                        if (!spentTXOs[input.id]) {
+                            spentTXOs[input.id] = [];
+                        }
+                        spentTXOs[input.id].push(input.index);
+                    }
+                }
+            }
+            return true;
+        },
+        this.get_last_block().hash);
+    }
+    async get_balance() {
+        let value = 0;
+        await this.get_utxo((transaction_id, index, vout) => {
+            value += vout.amount;
+            return true;
+        });
+        return value;
+    }
+    async create_transaction(to, amount) {
+        let value = 0;
+        let input = [];
+        let output = [];
+        let self = this;
+        let tx = null;
+        await this.get_utxo((transaction_id, index, vout) => {
+            value += vout.amount;
+            let signature = Crypto.sign(self.get_account_keypair(), JSON.stringify(vout));
+            input.push(new TxInput(transaction_id, index, signature));
+            if (value >= amount) {
+                output.push(new TxOutput(amount, to));
+                if (value > amount)
+                    output.push(new TxOutput(value - amount, self.get_public_key()));
+                tx = new Transaction(input, output);
+                // stop
+                return false;
+            }
+            return true;
+        });
+        if (value < amount) {
+            throw new Error("amount is not enough!");
+        }
+        if (tx == null) {
+            throw new Error("create transaction failed!");
+        }
+        this.tx_pool[tx.id] = tx;
+        this.broadcast(Msg.transaction(tx));
+
+        return tx;
+    }
 }
 
 module.exports = BlockChain;
\ No newline at end of file
diff --git a/src/js/crypto.js b/src/js/crypto.js
new file mode 100644
index 0000000..5293a3c
--- /dev/null
+++ b/src/js/crypto.js
@@ -0,0 +1,23 @@
+'use strict';
+
+var crypto = require("crypto");
+var ed = require("ed25519");
+
+function calc_hash(data) {
+    return crypto.createHash('sha256').update(data).digest('hex');
+}
+
+function sign(keypair, data) {
+    return ed.Sign(Buffer.from(data, 'utf-8'), keypair).toString('hex');
+}
+
+function verify_signature(data, signature, publickey) {
+    var res = ed.Verify(Buffer.from(data, 'utf-8'), Buffer.from(signature, 'hex'), Buffer.from(publickey, 'hex'));
+    return res;
+}
+
+module.exports = {
+    calc_hash,
+    sign,
+    verify_signature
+};
\ No newline at end of file
diff --git a/src/js/genesis_block.json b/src/js/genesis_block.json
index e2afba1..0ac5c6f 100644
--- a/src/js/genesis_block.json
+++ b/src/js/genesis_block.json
@@ -8,5 +8,5 @@
     "hash": "d611edb9fd86ee234cdc08d9bf382330d6ccc721cd5e59cf2a01b0a2a8decfff",
     "block_signature": "603b61b14348fb7eb087fe3267e28abacadf3932f0e33958fb016ab60f825e3124bfe6c7198d38f8c91b0a3b1f928919190680e44fbe7289a4202039ffbb2109",
     "consensus_data": {},
-    "transcations": []
+    "transactions": []
 }
\ No newline at end of file
diff --git a/src/js/message.js b/src/js/message.js
index 7e9e58c..96ca6eb 100644
--- a/src/js/message.js
+++ b/src/js/message.js
@@ -15,5 +15,6 @@ module.exports = {
     block: (data) => { return { type: MessageType.Block, data: data }; },
     preprepare: (data) => { return { type: MessageType.PrePrepare, data: data }; },
     prepare: (data) => { return { type: MessageType.Prepare, data: data }; },
-    commit: (data) => { return { type: MessageType.Commit, data: data }; }
+    commit: (data) => { return { type: MessageType.Commit, data: data }; },
+    transaction: (data)=>{return { type: MessageType.Transaction, data: data }; }
 };
\ No newline at end of file
diff --git a/src/js/package.json b/src/js/package.json
index 26dcd3d..9308771 100644
--- a/src/js/package.json
+++ b/src/js/package.json
@@ -9,7 +9,8 @@
         "ed25519": "0.0.4",
         "eslint": "^5.13.0",
         "eslint-plugin-html": "^5.0.0",
-        "js-sha256": "^0.9.0"
+        "js-sha256": "^0.9.0",
+        "level": "^4.0.0"
     },
     "devDependencies": {},
     "scripts": {
diff --git a/src/js/test/create_genesis.js b/src/js/test/create_genesis.js
index 61b8eac..a79e3ea 100644
--- a/src/js/test/create_genesis.js
+++ b/src/js/test/create_genesis.js
@@ -18,12 +18,12 @@ let genesis = {
     "hash": null,
     "block_signature": null,
     "consensus_data": {},
-    "transcations": []
+    "transactions": []
 };
 
 function prepare_data() {
     let tx = "";
-    genesis.transcations.forEach(val => {
+    genesis.transactions.forEach(val => {
         tx += val.toString('utf8');
     });
     let data = genesis.version.toString()
diff --git a/src/js/test/db.js b/src/js/test/db.js
new file mode 100644
index 0000000..01e7db8
--- /dev/null
+++ b/src/js/test/db.js
@@ -0,0 +1,34 @@
+'use strict';
+
+var crypto = require('crypto');
+var ed = require('ed25519');
+var BlockChain = require("../blockchain");
+var Consensus = require("../consensus/dpos");
+
+var password = 'I am tester!';
+
+var hash = crypto.createHash('sha256').update(password).digest();
+var keypair = ed.MakeKeypair(hash);
+
+let blockchains = [];
+for (var i = 0; i < 20; ++i) {
+    let blockchain = new BlockChain(Consensus, keypair, i);
+    blockchain.start();
+    blockchains.push(blockchain);
+}
+
+// setTimeout(() => {
+//     for (var i = 0; i < 20; ++i) {
+//         console.log(`${i} --> ${blockchains[i].list_peers()}`);
+//     }
+// }, 3000);
+
+setTimeout(async () => {
+    console.log("=================");
+    await blockchains[0].iterator_forward((block) => {
+        console.log("-----------------");
+        console.log(block.height);
+        console.log(block.hash);
+        return true;
+    }, blockchains[0].get_last_block().hash);
+}, 5000);
\ No newline at end of file
diff --git a/src/js/test/transaction.js b/src/js/test/transaction.js
new file mode 100644
index 0000000..7ff8dbb
--- /dev/null
+++ b/src/js/test/transaction.js
@@ -0,0 +1,40 @@
+'use strict';
+
+var crypto = require('crypto');
+var ed = require('ed25519');
+var BlockChain = require("../blockchain");
+var Consensus = require("../consensus/dpos");
+
+
+let blockchains = [];
+for (var i = 0; i < 20; ++i) {
+
+    var password = `I am tester ${i}!`;
+    var hash = crypto.createHash('sha256').update(password).digest();
+    var keypair = ed.MakeKeypair(hash);
+    console.log(`node ${i} address: ${keypair.publicKey.toString('hex')}`);
+
+    let blockchain = new BlockChain(Consensus, keypair, i);
+    blockchain.start();
+    blockchains.push(blockchain);
+}
+
+// setTimeout(() => {
+//     for (var i = 0; i < 20; ++i) {
+//         console.log(`${i} --> ${blockchains[i].list_peers()}`);
+//     }
+// }, 3000);
+
+setTimeout(() => {
+    let address = blockchains[6].get_public_key();
+    blockchains[0].create_transaction(address, 30);
+}, 3000);
+
+async function get_balance() {
+    let amount = await blockchains[0].get_balance();
+    console.log(`node 0 balance: ${amount}`);
+    amount = await blockchains[6].get_balance();
+    console.log(`node 6 balance: ${amount}`);
+}
+
+setInterval(get_balance, 10000);
diff --git a/src/js/transaction.js b/src/js/transaction.js
index 0616fde..1e271c5 100644
--- a/src/js/transaction.js
+++ b/src/js/transaction.js
@@ -1,13 +1,64 @@
 'use strict';
+var Crypto = require("./crypto");
 
-class Transaction {
-    constructor() {
-
+class TxOutput {
+    constructor(amount, ScriptPubKey) {
+        this.amount_ = amount;
+        this.script_pubkey_ = ScriptPubKey;
     }
-
-    static verify(tx) {
-        return true;
+    toObject() {
+        let output = {
+            "amount": this.amount_,
+            "ScriptPubKey": this.script_pubkey_
+        };
+        return output;
     }
 }
 
-module.exports = Transaction;
\ No newline at end of file
+class TxInput {
+    constructor(id, index, ScriptSig) {
+        this.id_ = id;
+        this.index_ = index;
+        this.script_sig_ = ScriptSig;
+    }
+    toObject() {
+        let input = {
+            "id": this.id_,
+            "index": this.index_,
+            "ScriptSig": this.script_sig_
+        };
+        return input;
+    }
+}
+
+class Transaction {
+    constructor(input, output) {
+        this.input_ = [];
+        for (i = 0; i < input.length; ++i) {
+            this.input_.push(input[i].toObject());
+        }
+        this.output_ = [];
+        for (var i = 0; i < output.length; ++i) {
+            this.output_.push(output[i].toObject());
+        }
+        this.id_ = Crypto.calc_hash(JSON.stringify(this.input_) + JSON.stringify(this.output_));
+        return this.toObject();
+    }
+    get_id() { return this.id_; }
+    get_input() { return this.input_; }
+    get_output() { return this.output_; }
+    toObject() {
+        let tx = {
+            "id": this.id_,
+            "input": this.input_,
+            "output": this.output_
+        };
+        return tx;
+    }
+}
+
+module.exports = {
+    TxOutput,
+    TxInput,
+    Transaction
+};
\ No newline at end of file