diff --git a/python/paddle/v2/fluid/tests/book/test_fit_a_line.py b/python/paddle/v2/fluid/tests/book/test_fit_a_line.py
index 27f34b17339db31ef3c07555db946fa76d6f1922..06860a2a465c6f8590336670372eb6ff43b10594 100644
--- a/python/paddle/v2/fluid/tests/book/test_fit_a_line.py
+++ b/python/paddle/v2/fluid/tests/book/test_fit_a_line.py
@@ -16,6 +16,8 @@ import paddle.v2 as paddle
 import paddle.v2.fluid as fluid
 import contextlib
 import unittest
+import math
+import sys
 
 
 def main(use_cuda):
@@ -58,6 +60,8 @@ def main(use_cuda):
             print(avg_loss_value)
             if avg_loss_value[0] < 10.0:
                 return
+            if math.isnan(float(avg_loss_value)):
+                sys.exit("got NaN loss, training failed.")
     raise AssertionError("Fit a line cost is too large, {0:2.2}".format(
         avg_loss_value[0]))
 
diff --git a/python/paddle/v2/fluid/tests/book/test_image_classification_train.py b/python/paddle/v2/fluid/tests/book/test_image_classification_train.py
index 03b009ebb0714a91329a1c56ff3939beecb03435..ffbe5bdbd646a03884868df659eb9d0089f9479e 100644
--- a/python/paddle/v2/fluid/tests/book/test_image_classification_train.py
+++ b/python/paddle/v2/fluid/tests/book/test_image_classification_train.py
@@ -17,6 +17,8 @@ from __future__ import print_function
 import paddle.v2 as paddle
 import paddle.v2.fluid as fluid
 import contextlib
+import math
+import sys
 import numpy
 import unittest
 
@@ -145,6 +147,8 @@ def train(net_type, use_cuda, save_dirname):
                     loss_t, acc_t = exe.run(program=test_program,
                                             feed=feeder.feed(test_data),
                                             fetch_list=[avg_cost, acc])
+                    if math.isnan(float(loss_t)):
+                        sys.exit("got NaN loss, training failed.")
                     acc_list.append(float(acc_t))
                     avg_loss_list.append(float(loss_t))
                     break  # Use 1 segment for speeding up CI
diff --git a/python/paddle/v2/fluid/tests/book/test_recognize_digits.py b/python/paddle/v2/fluid/tests/book/test_recognize_digits.py
index fb6b1f7192d51dcd654543e4c4ae5ee0c6fe060f..c3f6877575488e6e76602a5641d648171b8815f4 100644
--- a/python/paddle/v2/fluid/tests/book/test_recognize_digits.py
+++ b/python/paddle/v2/fluid/tests/book/test_recognize_digits.py
@@ -18,6 +18,8 @@ import paddle.v2 as paddle
 import sys
 import numpy
 import unittest
+import math
+import sys
 
 
 def parse_arg():
@@ -148,6 +150,8 @@ def train(nn_type, use_cuda, parallel, save_dirname):
                         'PassID {0:1}, BatchID {1:04}, Test Loss {2:2.2}, Acc {3:2.2}'.
                         format(pass_id, batch_id + 1,
                                float(avg_loss_val), float(acc_val)))
+                    if math.isnan(float(avg_loss_val)):
+                        sys.exit("got NaN loss, training failed.")
     raise AssertionError("Loss of recognize digits is too large")
 
 
diff --git a/python/paddle/v2/fluid/tests/book/test_recommender_system.py b/python/paddle/v2/fluid/tests/book/test_recommender_system.py
index d4a694e5721415fd9c953a83d927b25b80f5fb47..9c7ab7d6318472ac9378dd1966b75d19b5505bf5 100644
--- a/python/paddle/v2/fluid/tests/book/test_recommender_system.py
+++ b/python/paddle/v2/fluid/tests/book/test_recommender_system.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import math
+import sys
 import numpy as np
 import paddle.v2 as paddle
 import paddle.v2.fluid.core as core
@@ -217,6 +219,8 @@ def main():
             if out[0] < 6.0:
                 # if avg cost less than 6.0, we think our code is good.
                 exit(0)
+            if math.isnan(float(out[0])):
+                sys.exit("got NaN loss, training failed.")
 
 
 main()
diff --git a/python/paddle/v2/fluid/tests/book/test_understand_sentiment.py b/python/paddle/v2/fluid/tests/book/test_understand_sentiment.py
index 2ba9077a26202b1c16cc480823115f7ad55c2c67..9c5cb667aed7456b54d32dcd650852cfdbd6cce1 100644
--- a/python/paddle/v2/fluid/tests/book/test_understand_sentiment.py
+++ b/python/paddle/v2/fluid/tests/book/test_understand_sentiment.py
@@ -16,6 +16,8 @@ import unittest
 import paddle.v2.fluid as fluid
 import paddle.v2 as paddle
 import contextlib
+import math
+import sys
 
 
 def convolution_net(data, label, input_dim, class_dim=2, emb_dim=32,
@@ -115,6 +117,8 @@ def main(word_dict, net_method, use_cuda):
             print("cost=" + str(cost_val) + " acc=" + str(acc_val))
             if cost_val < 0.4 and acc_val > 0.8:
                 return
+            if math.isnan(float(cost_val)):
+                sys.exit("got NaN loss, training failed.")
     raise AssertionError("Cost is too large for {0}".format(
         net_method.__name__))
 
diff --git a/python/paddle/v2/fluid/tests/book/test_word2vec.py b/python/paddle/v2/fluid/tests/book/test_word2vec.py
index 766ba9681d1bb816170e0458f540b32511c02933..f013d7f1551bdbfb2f725809e2fb4d7d686560fe 100644
--- a/python/paddle/v2/fluid/tests/book/test_word2vec.py
+++ b/python/paddle/v2/fluid/tests/book/test_word2vec.py
@@ -16,6 +16,8 @@ import paddle.v2 as paddle
 import paddle.v2.fluid as fluid
 import unittest
 import os
+import math
+import sys
 
 
 def main(use_cuda, is_sparse, parallel):
@@ -112,6 +114,9 @@ def main(use_cuda, is_sparse, parallel):
                                   fetch_list=[avg_cost])
             if avg_cost_np[0] < 5.0:
                 return
+            if math.isnan(float(avg_cost_np[0])):
+                sys.exit("got NaN loss, training failed.")
+
     raise AssertionError("Cost is too large {0:2.2}".format(avg_cost_np[0]))