diff --git a/paddle/fluid/framework/details/threaded_ssa_graph_executor.cc b/paddle/fluid/framework/details/threaded_ssa_graph_executor.cc
index 07097c7e75c6ce638549716cd6523f387cdefd92..bad9a6b2ba1cb2f61a1314c0bb59b9d35858d23f 100644
--- a/paddle/fluid/framework/details/threaded_ssa_graph_executor.cc
+++ b/paddle/fluid/framework/details/threaded_ssa_graph_executor.cc
@@ -168,7 +168,13 @@ void ThreadedSSAGraphExecutor::InsertFetchOps(
 
   for (size_t i = 0; i < fetch_tensors.size(); ++i) {
     auto &var_name = fetch_tensors[i];
-    auto &vars = fetched_vars.at(var_name);
+
+    auto fetched_var_it = fetched_vars.find(var_name);
+    PADDLE_ENFORCE(fetched_var_it != fetched_vars.end(),
+                   "Cannot find fetched variable.(Perhaps the main_program "
+                   "is not set to ParallelExecutor)");
+
+    auto &vars = fetched_var_it->second;
     auto *op = new FetchOpHandle(fetch_data, i, &local_scopes_);
     fetch_ops->emplace_back(op);
 
diff --git a/python/paddle/fluid/tests/demo/pyreader.py b/python/paddle/fluid/tests/demo/pyreader.py
index a7550fd1f13948d2279c4de2ee0f69af56701c84..47b20a0c5c8e0c7e49c67e77a27587acdc080ee0 100644
--- a/python/paddle/fluid/tests/demo/pyreader.py
+++ b/python/paddle/fluid/tests/demo/pyreader.py
@@ -36,7 +36,7 @@ def network(is_train):
 
     prediction = fluid.layers.fc(input=hidden, size=10, act='softmax')
     loss = fluid.layers.cross_entropy(input=prediction, label=label)
-    return fluid.layers.mean(loss), queue
+    return fluid.layers.mean(loss), queue, reader
 
 
 def pipe_reader_to_queue(reader_creator, queue):
@@ -70,27 +70,46 @@ def main():
 
     with fluid.program_guard(train_prog, startup_prog):
         with fluid.unique_name.guard():
-            loss, train_queue = network(True)
+            loss, train_queue, train_reader = network(True)
             adam = fluid.optimizer.Adam(learning_rate=0.01)
             adam.minimize(loss)
 
     test_prog = fluid.Program()
     with fluid.program_guard(test_prog, fluid.Program()):
         with fluid.unique_name.guard():
-            test_loss, test_queue = network(False)
+            test_loss, test_queue, test_reader = network(False)
 
     fluid.Executor(fluid.CUDAPlace(0)).run(startup_prog)
 
-    trainer = fluid.ParallelExecutor(use_cuda=True, loss_name=loss.name)
-    tester = fluid.ParallelExecutor(use_cuda=True, share_vars_from=trainer)
+    trainer = fluid.ParallelExecutor(
+        use_cuda=True, loss_name=loss.name, main_program=train_prog)
+
+    tester = fluid.ParallelExecutor(
+        use_cuda=True, share_vars_from=trainer, main_program=test_prog)
 
     for epoch_id in xrange(10):
-        pipe_reader_to_queue(paddle.batch(mnist.train(), 32), train_queue)
-        pipe_reader_to_queue(paddle.batch(mnist.test(), 32), test_queue)
+        train_data_thread = pipe_reader_to_queue(
+            paddle.batch(mnist.train(), 32), train_queue)
         try:
-            print 'train_loss', numpy.array(trainer.run(fetch_list=[loss.name]))
+            while True:
+                print 'train_loss', numpy.array(
+                    trainer.run(fetch_list=[loss.name]))
         except fluid.core.EOFException:
             print 'End of epoch', epoch_id
+            train_reader.reset()
+        train_data_thread.join()
+
+        test_data_thread = pipe_reader_to_queue(
+            paddle.batch(mnist.train(), 32), test_queue)
+        try:
+            while True:
+                print numpy.array(tester.run(fetch_list=[test_loss.name]))
+        except fluid.core.EOFException:
+            print 'End of testing'
+            test_reader.reset()
+
+        test_data_thread.join()
+        break
 
 
 if __name__ == '__main__':