diff --git a/deepLearning/08_dbn.py b/deepLearning/08_dbn.py
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+++ b/deepLearning/08_dbn.py
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+"""
+Deep Belief Network
+author: Ye Hu
+2016/12/20
+redit：wanyouwen 2018/05/02
+"""
+import timeit
+import numpy as np
+import tensorflow as tf
+import input_data
+from logisticRegression import LogisticRegression
+from mlp import HiddenLayer
+from rbm import RBM
+
+class DBN(object):
+    """
+    An implement of deep belief network
+    The hidden layers are firstly pretrained by RBM, then DBN is treated as a normal
+    MLP by adding a output layer.
+    """
+    def __init__(self, n_in=784, n_out=10, hidden_layers_sizes=[500, 500]):
+        """
+        :param n_in: int, the dimension of input
+        :param n_out: int, the dimension of output
+        :param hidden_layers_sizes: list or tuple, the hidden layer sizes
+        """
+        # Number of layers
+        assert len(hidden_layers_sizes) > 0
+        self.n_layers = len(hidden_layers_sizes)
+        self.layers = []    # normal sigmoid layer
+        self.rbm_layers = []   # RBM layer
+        self.params = []       # keep track of params for training
+
+        # Define the input and output
+        self.x = tf.placeholder(tf.float32, shape=[None, n_in])
+        self.y = tf.placeholder(tf.float32, shape=[None, n_out])
+
+        # Contruct the layers of DBN
+        for i in range(self.n_layers):
+            if i == 0:
+                layer_input = self.x
+                input_size = n_in
+            else:
+                layer_input = self.layers[i-1].output
+                input_size = hidden_layers_sizes[i-1]
+            # Sigmoid layer
+            sigmoid_layer = HiddenLayer(inpt=layer_input, n_in=input_size, n_out=hidden_layers_sizes[i],
+                                    activation=tf.nn.sigmoid)
+            self.layers.append(sigmoid_layer)
+            # Add the parameters for finetuning
+            self.params.extend(sigmoid_layer.params)
+            # Create the RBM layer
+            self.rbm_layers.append(RBM(inpt=layer_input, n_visiable=input_size, n_hidden=hidden_layers_sizes[i],
+                                        W=sigmoid_layer.W, hbias=sigmoid_layer.b))
+        # We use the LogisticRegression layer as the output layer
+        self.output_layer = LogisticRegression(inpt=self.layers[-1].output, n_in=hidden_layers_sizes[-1],
+                                                n_out=n_out)
+        self.params.extend(self.output_layer.params)
+        # The finetuning cost
+        self.cost = self.output_layer.cost(self.y)
+        # The accuracy
+        self.accuracy = self.output_layer.accuarcy(self.y)
+    
+    def pretrain(self, sess, X_train, batch_size=50, pretraining_epochs=10, lr=0.1, k=1, 
+                    display_step=1):
+        """
+        Pretrain the layers (just train the RBM layers)
+        :param sess: tf.Session
+        :param X_train: the input of the train set (You might modidy this function if you do not use the desgined mnist)
+        :param batch_size: int
+        :param lr: float
+        :param k: int, use CD-k
+        :param pretraining_epoch: int
+        :param display_step: int
+        """
+        print('Starting pretraining...\n')
+        start_time = timeit.default_timer()
+        batch_num = int(X_train.train.num_examples / batch_size)
+        # Pretrain layer by layer
+        for i in range(self.n_layers):
+            cost = self.rbm_layers[i].get_reconstruction_cost()
+            train_ops = self.rbm_layers[i].get_train_ops(learning_rate=lr, k=k, persistent=None)
+            for epoch in range(pretraining_epochs):
+                avg_cost = 0.0
+                for j in range(batch_num):
+                    x_batch, _ = X_train.train.next_batch(batch_size)
+                    # 训练
+                    sess.run(train_ops, feed_dict={self.x: x_batch})
+                    # 计算cost
+                    avg_cost += sess.run(cost, feed_dict={self.x: x_batch,}) / batch_num
+                # 输出
+                if epoch % display_step == 0:
+                    print("\tPretraing layer {0} Epoch {1} cost: {2}".format(i, epoch, avg_cost))
+
+        end_time = timeit.default_timer()
+        print("\nThe pretraining process ran for {0} minutes".format((end_time - start_time) / 60))
+    
+    def finetuning(self, sess, trainSet, training_epochs=10, batch_size=100, lr=0.1,
+                   display_step=1):
+        """
+        Finetuing the network
+        """
+        print("\nStart finetuning...\n")
+        start_time = timeit.default_timer()
+        train_op = tf.train.GradientDescentOptimizer(learning_rate=lr).minimize(
+            self.cost, var_list=self.params)
+        for epoch in range(training_epochs):
+            avg_cost = 0.0
+            batch_num = int(trainSet.train.num_examples / batch_size)
+            for i in range(batch_num):
+                x_batch, y_batch = trainSet.train.next_batch(batch_size)
+                # 训练
+                sess.run(train_op, feed_dict={self.x: x_batch, self.y: y_batch})
+                # 计算cost
+                avg_cost += sess.run(self.cost, feed_dict=
+                {self.x: x_batch, self.y: y_batch}) / batch_num
+            # 输出
+            if epoch % display_step == 0:
+                val_acc = sess.run(self.accuracy, feed_dict={self.x: trainSet.validation.images,
+                                                       self.y: trainSet.validation.labels})
+                print("\tEpoch {0} cost: {1}, validation accuacy: {2}".format(epoch, avg_cost, val_acc))
+
+        end_time = timeit.default_timer()
+        print("\nThe finetuning process ran for {0} minutes".format((end_time - start_time) / 60))
+
+if __name__ == "__main__":
+    # mnist examples
+    mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)
+    dbn = DBN(n_in=784, n_out=10, hidden_layers_sizes=[500, 500, 500])
+    sess = tf.Session()
+    init = tf.global_variables_initializer()
+    sess.run(init)
+    # set random_seed
+    tf.set_random_seed(seed=1111)
+    dbn.pretrain(sess, X_train=mnist)
+    dbn.finetuning(sess, trainSet=mnist)