diff --git a/python/examples/pipeline/imdb_model_ensemble/test_pipeline_server.py b/python/examples/pipeline/imdb_model_ensemble/test_pipeline_server.py
index 3f96f619608c608aa4e21c22be8f05da218ae3a7..8ff147eb488ca7c2b8e17007c6e3596762ec0203 100644
--- a/python/examples/pipeline/imdb_model_ensemble/test_pipeline_server.py
+++ b/python/examples/pipeline/imdb_model_ensemble/test_pipeline_server.py
@@ -22,21 +22,19 @@ from paddle_serving_app.reader import IMDBDataset
 logging.basicConfig(
     format='%(asctime)s %(levelname)-8s [%(filename)s:%(lineno)d] %(message)s',
     datefmt='%Y-%m-%d %H:%M',
-    # level=logging.DEBUG)
     level=logging.INFO)
 
 
 class ImdbOp(Op):
+    def load_user_resources(self):
+        self.imdb_dataset = IMDBDataset()
+        self.imdb_dataset.load_resource('imdb.vocab')
+
     def preprocess(self, input_data):
         data = input_data.parse()
-        imdb_dataset = IMDBDataset()
-        imdb_dataset.load_resource('imdb.vocab')
-        word_ids, _ = imdb_dataset.get_words_and_label(data['words'])
+        word_ids, _ = self.imdb_dataset.get_words_and_label(data['words'])
         return {"words": word_ids}
 
-    # def postprocess(self, fetch_data):
-    # return {key: str(value) for key, value in fetch_data.items()}
-
 
 class CombineOp(Op):
     def preprocess(self, input_data):
@@ -45,7 +43,7 @@ class CombineOp(Op):
             data = channeldata.parse()
             logging.info("{}: {}".format(op_name, data["prediction"]))
             combined_prediction += data["prediction"]
-        data = {"prediction": str(combined_prediction / 2)}
+        data = {"prediction": combined_prediction / 2}
         return data
 
 
@@ -77,7 +75,7 @@ combine_op = CombineOp(
 
 server = PipelineServer()
 server.add_ops([read_op, bow_op, cnn_op, combine_op])
-# server.set_response_op(bow_op)
+#server.set_response_op(bow_op)
 server.set_response_op(combine_op)
 server.prepare_server('config.yml')
 server.run_server()
diff --git a/python/pipeline/channel.py b/python/pipeline/channel.py
index 2a1d82d7558262d294e3e345583b34ec97fd6031..cbe81249817e7ba21928398b1ca0b502ed098530 100644
--- a/python/pipeline/channel.py
+++ b/python/pipeline/channel.py
@@ -34,7 +34,8 @@ class ChannelDataEcode(enum.Enum):
     NOT_IMPLEMENTED = 2
     TYPE_ERROR = 3
     RPC_PACKAGE_ERROR = 4
-    UNKNOW = 5
+    CLIENT_ERROR = 5
+    UNKNOW = 6
 
 
 class ChannelDataType(enum.Enum):
diff --git a/python/pipeline/operator.py b/python/pipeline/operator.py
index b13408d2c214296d60e51b2d41dff08e8c34c5c8..230ffbd4bb3ca4050bfe2c0f49b06c8c43e4c682 100644
--- a/python/pipeline/operator.py
+++ b/python/pipeline/operator.py
@@ -204,6 +204,9 @@ class Op(object):
             threads.append(t)
         return threads
 
+    def load_user_resources(self):
+        pass
+
     def _run(self, concurrency_idx, input_channel, output_channels,
              client_type):
         def get_log_func(op_info_prefix):
@@ -220,6 +223,9 @@ class Op(object):
         self.init_client(client_type, self._client_config,
                          self._server_endpoints, self._fetch_names)
 
+        # load user resources
+        self.load_user_resources()
+
         self._is_run = True
         while self._is_run:
             self._profiler_record("{}-get#{}_0".format(op_info_prefix, tid))
@@ -319,6 +325,16 @@ class Op(object):
                     continue
                 self._profiler_record("{}-midp#{}_1".format(op_info_prefix,
                                                             tid))
+                # op client return None
+                if midped_data is None:
+                    self._push_to_output_channels(
+                        ChannelData(
+                            ecode=ChannelDataEcode.CLIENT_ERROR.value,
+                            error_info=log(
+                                "predict failed. pls check the server side."),
+                            data_id=data_id),
+                        output_channels)
+                    continue
             else:
                 midped_data = preped_data
 
diff --git a/python/pipeline/pipeline_client.py b/python/pipeline/pipeline_client.py
index 06b6944366a5684960695271545ac9edbbfb291b..7e9af1617392eda5770b11afa7a6e8d6da3b8b88 100644
--- a/python/pipeline/pipeline_client.py
+++ b/python/pipeline/pipeline_client.py
@@ -14,6 +14,7 @@
 # pylint: disable=doc-string-missing
 import grpc
 import numpy as np
+from numpy import array
 from .proto import pipeline_service_pb2
 from .proto import pipeline_service_pb2_grpc
 
@@ -51,5 +52,10 @@ class PipelineClient(object):
         for idx, key in enumerate(resp.key):
             if key not in fetch:
                 continue
-            fetch_map[key] = resp.value[idx]
+            data = resp.value[idx]
+            try:
+                data = eval(resp.value[idx])
+            except Exception as e:
+                pass
+            fetch_map[key] = data
         return fetch_map
diff --git a/python/pipeline/pipeline_server.py b/python/pipeline/pipeline_server.py
index 904139467d771f0f31e2b60d29eff11a64df24e7..94d517fc3ebadd8f1e71e7257763161e51b92355 100644
--- a/python/pipeline/pipeline_server.py
+++ b/python/pipeline/pipeline_server.py
@@ -140,18 +140,26 @@ class PipelineService(pipeline_service_pb2_grpc.PipelineServiceServicer):
         if resp.ecode == ChannelDataEcode.OK.value:
             if channeldata.datatype == ChannelDataType.CHANNEL_NPDATA.value:
                 feed = channeldata.parse()
+                # ndarray to string
                 for name, var in feed.items():
-                    resp.value.append(var.tostring())  #TODO: no shape and type
+                    resp.value.append(var.__repr__())
                     resp.key.append(name)
             elif channeldata.datatype == ChannelDataType.DICT.value:
                 feed = channeldata.parse()
                 for name, var in feed.items():
-                    resp.value.append(str(var))
+                    if not isinstance(var, str):
+                        resp.ecode = ChannelDataEcode.TYPE_ERROR.value
+                        resp.error_info = self._log(
+                            "fetch var type must be str({}).".format(
+                                type(var)))
+                        break
+                    resp.value.append(var)
                     resp.key.append(name)
             else:
-                raise TypeError(
-                    self._log("Error type({}) in datatype.".format(
-                        channeldata.datatype)))
+                resp.ecode = ChannelDataEcode.TYPE_ERROR.value
+                resp.error_info = self._log(
+                    "Error type({}) in datatype.".format(channeldata.datatype))
+                logging.error(resp.error_info)
         else:
             resp.error_info = channeldata.error_info
         return resp