diff --git a/demo/mnist/api_train_v2.py b/demo/mnist/api_train_v2.py
index 6439d07ac6157dbbe505c1a3f59bda1b681ee2ae..341a7165da4e2f6bce1d37bfecb9b58abedc44a1 100644
--- a/demo/mnist/api_train_v2.py
+++ b/demo/mnist/api_train_v2.py
@@ -63,6 +63,8 @@ def main():
     label = paddle.layer.data(
         name='label', type=paddle.data_type.integer_value(10))
 
+    # Here we can build the prediction network in different ways. Please
+    # choose one by uncomment corresponding line.
     predict = softmax_regression(images)
     #predict = multilayer_perceptron(images)
     #predict = convolutional_neural_network(images)
@@ -80,14 +82,20 @@ def main():
                                  parameters=parameters,
                                  update_equation=optimizer)
 
+    list = []
+
     def event_handler(event):
         if isinstance(event, paddle.event.EndIteration):
             if event.batch_id % 100 == 0:
-                result = trainer.test(reader=paddle.reader.batched(
-                    paddle.dataset.mnist.test(), batch_size=128))
-                print "Pass %d, Batch %d, Cost %f, %s, Testing metrics %s" % (
-                    event.pass_id, event.batch_id, event.cost, event.metrics,
-                    result.metrics)
+                print "Pass %d, Batch %d, Cost %f, %s" % (
+                    event.pass_id, event.batch_id, event.cost, event.metrics)
+        if isinstance(event, paddle.event.EndPass):
+            result = trainer.test(reader=paddle.reader.batched(
+                paddle.dataset.mnist.test(), batch_size=128))
+            print "Test with Pass %d, Cost %f, %s\n" % (
+                event.pass_id, event.cost, result.metrics)
+            list.append((event.pass_id, event.cost,
+                         result.metrics['classification_error_evaluator']))
 
     trainer.train(
         reader=paddle.reader.batched(
@@ -97,10 +105,15 @@ def main():
         event_handler=event_handler,
         num_passes=100)
 
+    # find the best pass
+    best = sorted(list, key=lambda list: float(list[1]))[0]
+    print 'Best pass is %s, testing Avgcost is %s' % (best[0], best[1])
+    print 'The classification accuracy is %.2f%%' % (100 - float(best[2]) * 100)
+
     # output is a softmax layer. It returns probabilities.
     # Shape should be (100, 10)
     probs = paddle.infer(
-        output=inference,
+        output=predict,
         parameters=parameters,
         reader=paddle.reader.batched(
             paddle.reader.firstn(
diff --git a/python/paddle/v2/event.py b/python/paddle/v2/event.py
index a78bcf076cc65e0dfdfc5760e099900418162f35..6a7bcb81879c0a364a1d896071055a6247e96c19 100644
--- a/python/paddle/v2/event.py
+++ b/python/paddle/v2/event.py
@@ -52,8 +52,9 @@ class EndPass(WithMetric):
     Event On One Pass Training Complete.
     """
 
-    def __init__(self, pass_id, evaluator):
+    def __init__(self, pass_id, cost, evaluator):
         self.pass_id = pass_id
+        self.cost = cost
         WithMetric.__init__(self, evaluator)
 
 
diff --git a/python/paddle/v2/trainer.py b/python/paddle/v2/trainer.py
index e743a49523ff21627ea2abfb76cee8b9ffd685e2..a4ef0df597dd7f52833a0176333dabc93d02c18d 100644
--- a/python/paddle/v2/trainer.py
+++ b/python/paddle/v2/trainer.py
@@ -107,6 +107,8 @@ class SGD(ITrainer):
             event_handler(v2_event.BeginPass(pass_id))
             pass_evaluator.start()
             updater.startPass()
+            total_cost_sum = 0
+            total_batch = 0
             for batch_id, data_batch in enumerate(reader()):
                 pass_type = updater.startBatch(len(data_batch))
                 self.__gradient_machine__.forwardBackward(
@@ -127,6 +129,8 @@ class SGD(ITrainer):
                 cost_vec = out_args.getSlotValue(0)
                 cost_vec = cost_vec.copyToNumpyMat()
                 cost = cost_vec.sum() / len(data_batch)
+                total_cost_sum += cost_vec.sum()
+                total_batch += len(data_batch)
                 updater.finishBatch(cost)
                 batch_evaluator.finish()
                 event_handler(
@@ -138,7 +142,11 @@ class SGD(ITrainer):
 
             updater.finishPass()
             pass_evaluator.finish()
-            event_handler(v2_event.EndPass(pass_id, evaluator=pass_evaluator))
+            event_handler(
+                v2_event.EndPass(
+                    pass_id,
+                    cost=total_cost_sum / total_batch,
+                    evaluator=pass_evaluator))
         self.__gradient_machine__.finish()
 
     def default_reader_dict(self):