diff --git a/paddle/contrib/inference/CMakeLists.txt b/paddle/contrib/inference/CMakeLists.txt
index 6847f7db7fc0f6b41ced1260d409ca6eba9b53eb..8ca34465395761cab9cbde4bfbcf32edc1c4a1d1 100644
--- a/paddle/contrib/inference/CMakeLists.txt
+++ b/paddle/contrib/inference/CMakeLists.txt
@@ -18,32 +18,35 @@ if(APPLE)
 endif(APPLE)
 
 function(inference_api_test TARGET_NAME)
-    set(options "")
-    set(oneValueArgs "")
-    set(multiValueArgs ARGS)
-    cmake_parse_arguments(inference_test "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
+    if (WITH_TESTING)
+        set(options "")
+        set(oneValueArgs "")
+        set(multiValueArgs ARGS)
+        cmake_parse_arguments(inference_test "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
 
-    set(PYTHON_TESTS_DIR ${PADDLE_BINARY_DIR}/python/paddle/fluid/tests)
-    cc_test(test_paddle_inference_${TARGET_NAME}
-            SRCS test_paddle_inference_${TARGET_NAME}.cc
-            DEPS paddle_fluid_api paddle_inference_api
-            ARGS --dirname=${PYTHON_TESTS_DIR}/book/)
-    if(inference_test_ARGS)
-        set_tests_properties(test_paddle_inference_${TARGET_NAME}
-                 PROPERTIES DEPENDS "${inference_test_ARGS}")
-    endif()
+        set(PYTHON_TESTS_DIR ${PADDLE_BINARY_DIR}/python/paddle/fluid/tests)
+        cc_test(${TARGET_NAME}
+                SRCS ${TARGET_NAME}.cc
+                DEPS paddle_fluid paddle_inference_api
+                ARGS --dirname=${PYTHON_TESTS_DIR}/book/)
+        if(inference_test_ARGS)
+            set_tests_properties(${TARGET_NAME}
+                    PROPERTIES DEPENDS "${inference_test_ARGS}")
+        endif()
+    endif(WITH_TESTING)
 endfunction(inference_api_test)
 
-
 cc_library(paddle_inference_api
     SRCS paddle_inference_api.cc paddle_inference_api_impl.cc
     DEPS ${FLUID_CORE_MODULES} ${GLOB_OP_LIB})
 
-if(WITH_TESTING)
-    cc_test(test_paddle_inference_api
-            SRCS test_paddle_inference_api.cc
-            DEPS paddle_inference_api)
+cc_test(test_paddle_inference_api
+        SRCS test_paddle_inference_api.cc
+        DEPS paddle_inference_api)
 
-    inference_api_test(api_impl
-                       ARGS test_word2vec test_image_classification)
+inference_api_test(test_paddle_inference_api_impl
+                    ARGS test_word2vec test_image_classification)
+
+if(WITH_TESTING)
+    add_subdirectory(demo)
 endif()
diff --git a/paddle/contrib/inference/demo/CMakeLists.txt b/paddle/contrib/inference/demo/CMakeLists.txt
new file mode 100644
index 0000000000000000000000000000000000000000..7b0fa77ad13c19f177e5b2446bcda6551471e45f
--- /dev/null
+++ b/paddle/contrib/inference/demo/CMakeLists.txt
@@ -0,0 +1,16 @@
+# Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+inference_api_test(simple_on_word2vec ARGS test_word2vec)
diff --git a/paddle/contrib/inference/demo/simple_on_word2vec.cc b/paddle/contrib/inference/demo/simple_on_word2vec.cc
new file mode 100644
index 0000000000000000000000000000000000000000..165d2e196b3d544f540cf72d61c6f9d0dfa62977
--- /dev/null
+++ b/paddle/contrib/inference/demo/simple_on_word2vec.cc
@@ -0,0 +1,71 @@
+/* Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License. */
+
+/*
+ * This file contains a simple demo for how to take a model for inference.
+ */
+
+#include <glog/logging.h>
+#include <gtest/gtest.h>
+#include <memory>
+#include "paddle/contrib/inference/paddle_inference_api.h"
+
+namespace paddle {
+namespace demo {
+
+DEFINE_string(dirname, "", "Directory of the inference model.");
+
+void Main(bool use_gpu) {
+  //# 1. Create PaddlePredictor with a config.
+  NativeConfig config;
+  config.model_dir = FLAGS_dirname + "word2vec.inference.model";
+  config.use_gpu = use_gpu;
+  config.fraction_of_gpu_memory = 0.15;
+  config.device = 0;
+  auto predictor =
+      CreatePaddlePredictor<NativeConfig, PaddleEngineKind::kNative>(config);
+
+  for (int batch_id = 0; batch_id < 3; batch_id++) {
+    //# 2. Prepare input.
+    int64_t data[4] = {1, 2, 3, 4};
+
+    PaddleBuf buf{.data = data, .length = sizeof(data)};
+    PaddleTensor tensor{.name = "",
+                        .shape = std::vector<int>({4, 1}),
+                        .data = buf,
+                        .dtype = PaddleDType::INT64};
+
+    // For simplicity, we set all the slots with the same data.
+    std::vector<PaddleTensor> slots(4, tensor);
+
+    //# 3. Run
+    std::vector<PaddleTensor> outputs;
+    CHECK(predictor->Run(slots, &outputs));
+
+    //# 4. Get output.
+    ASSERT_EQ(outputs.size(), 1);
+    LOG(INFO) << "output buffer size: " << outputs.front().data.length;
+    const size_t num_elements = outputs.front().data.length / sizeof(float);
+    // The outputs' buffers are in CPU memory.
+    for (size_t i = 0; i < std::min(5UL, num_elements); i++) {
+      LOG(INFO) << static_cast<float*>(outputs.front().data.data)[i];
+    }
+  }
+}
+
+TEST(demo, word2vec_cpu) { Main(false /*use_gpu*/); }
+TEST(demo, word2vec_gpu) { Main(true /*use_gpu*/); }
+
+}  // namespace demo
+}  // namespace paddle
diff --git a/paddle/contrib/inference/paddle_inference_api_impl.cc b/paddle/contrib/inference/paddle_inference_api_impl.cc
index 99a64662d4d04e3cf9dfdafe5b5ab9e5dac0af8a..e7a8fa68b7fa84e246c0860dcb6b5528eb155a66 100644
--- a/paddle/contrib/inference/paddle_inference_api_impl.cc
+++ b/paddle/contrib/inference/paddle_inference_api_impl.cc
@@ -248,9 +248,11 @@ CreatePaddlePredictor<NativeConfig, PaddleEngineKind::kNative>(
   VLOG(3) << "create NativePaddlePredictor";
   if (config.use_gpu) {
     // 1. GPU memeroy
-    PADDLE_ENFORCE(
-        config.fraction_of_gpu_memory > 0.f,
+    PADDLE_ENFORCE_GT(
+        config.fraction_of_gpu_memory,
+        0.f,
         "fraction_of_gpu_memory in the config should be set to range (0., 1.]");
+    PADDLE_ENFORCE_GE(config.device, 0, "Invalid device id %d", config.device);
     std::vector<std::string> flags;
     if (config.fraction_of_gpu_memory >= 0.0f ||
         config.fraction_of_gpu_memory <= 0.95f) {
diff --git a/paddle/contrib/inference/test_paddle_inference_api_impl.cc b/paddle/contrib/inference/test_paddle_inference_api_impl.cc
index 07b17acd484b13af2ab4019aafa4a08c6b9f59d4..1f960677163988be6f4c502738861bf86588f406 100644
--- a/paddle/contrib/inference/test_paddle_inference_api_impl.cc
+++ b/paddle/contrib/inference/test_paddle_inference_api_impl.cc
@@ -74,7 +74,7 @@ TEST(paddle_inference_api_impl, word2vec) {
   ASSERT_EQ(outputs.size(), 1UL);
   size_t len = outputs[0].data.length;
   float* data = static_cast<float*>(outputs[0].data.data);
-  for (int j = 0; j < len / sizeof(float); ++j) {
+  for (size_t j = 0; j < len / sizeof(float); ++j) {
     ASSERT_LT(data[j], 1.0);
     ASSERT_GT(data[j], -1.0);
   }
@@ -92,7 +92,7 @@ TEST(paddle_inference_api_impl, word2vec) {
   TestInference<platform::CPUPlace>(config.model_dir, cpu_feeds, cpu_fetchs1);
 
   float* lod_data = output1.data<float>();
-  for (size_t i = 0; i < output1.numel(); ++i) {
+  for (int i = 0; i < output1.numel(); ++i) {
     EXPECT_LT(lod_data[i] - data[i], 1e-3);
     EXPECT_GT(lod_data[i] - data[i], -1e-3);
   }