diff --git a/paddle/gserver/layers/ROIPoolLayer.cpp b/paddle/gserver/layers/ROIPoolLayer.cpp
index 131fd7e52bbed64aad063b5b96eb5d7c03d99d2d..99cfddb0cf3337745a716a8c329713c18b99eda3 100644
--- a/paddle/gserver/layers/ROIPoolLayer.cpp
+++ b/paddle/gserver/layers/ROIPoolLayer.cpp
@@ -91,6 +91,8 @@ void ROIPoolLayer::forward(PassType passType) {
   real* argmaxData = maxIdxs_->getData();
 
   for (size_t n = 0; n < numROIs; ++n) {
+    // the first five elememts of each RoI should be:
+    // batch_idx, roi_x_start, roi_y_start, roi_x_end, roi_y_end
     size_t roiBatchIdx = bottomROIs[0];
     size_t roiStartW = round(bottomROIs[1] * spatialScale_);
     size_t roiStartH = round(bottomROIs[2] * spatialScale_);
diff --git a/paddle/gserver/layers/ROIPoolLayer.h b/paddle/gserver/layers/ROIPoolLayer.h
index 796467a5c86e6374a64a457c8a6d259b054952d0..4f07e49d6fd1eda9fa7bd46e4cec771a75f571be 100644
--- a/paddle/gserver/layers/ROIPoolLayer.h
+++ b/paddle/gserver/layers/ROIPoolLayer.h
@@ -41,6 +41,7 @@ protected:
   size_t pooledHeight_;
   real spatialScale_;
 
+  // Since there is no int matrix, use real maxtrix instead.
   MatrixPtr maxIdxs_;
 
 public:
diff --git a/python/paddle/trainer/config_parser.py b/python/paddle/trainer/config_parser.py
index f31252882e516e447619822df6c980f308276ae2..43d02bf70e74c3903d50a4a2177059f4f474045a 100644
--- a/python/paddle/trainer/config_parser.py
+++ b/python/paddle/trainer/config_parser.py
@@ -1971,13 +1971,14 @@ class DetectionOutputLayer(LayerBase):
 
 @config_layer('roi_pool')
 class ROIPoolLayer(LayerBase):
-    def __init__(self, name, inputs, pooled_width, pooled_height,
-                 spatial_scale):
+    def __init__(self, name, inputs, pooled_width, pooled_height, spatial_scale,
+                 num_channels, **xargs):
         super(ROIPoolLayer, self).__init__(name, 'roi_pool', 0, inputs)
         config_assert(len(inputs) == 2, 'ROIPoolLayer must have 2 inputs')
         self.config.inputs[0].roi_pool_conf.pooled_width = pooled_width
         self.config.inputs[0].roi_pool_conf.pooled_height = pooled_height
         self.config.inputs[0].roi_pool_conf.spatial_scale = spatial_scale
+        self.set_cnn_layer(name, pooled_height, pooled_width, num_channels)
 
 
 @config_layer('data')
diff --git a/python/paddle/trainer_config_helpers/layers.py b/python/paddle/trainer_config_helpers/layers.py
index 623ca047cd91314864c0dd2d96ae31eea8e059ea..617fbff948bf03098eca4a31f44d4ff05e73dbcf 100644
--- a/python/paddle/trainer_config_helpers/layers.py
+++ b/python/paddle/trainer_config_helpers/layers.py
@@ -1345,7 +1345,8 @@ def roi_pool_layer(input,
         inputs=[input.name, rois.name],
         pooled_width=pooled_width,
         pooled_height=pooled_height,
-        spatial_scale=spatial_scale)
+        spatial_scale=spatial_scale,
+        num_channels=num_channels)
     return LayerOutput(
         name, LayerType.ROI_POOL_LAYER, parents=[input, rois], size=size)