diff --git a/docs/tutorials/pytorch2onnx.md b/docs/tutorials/pytorch2onnx.md
index 4930b6b3721..0b993455476 100644
--- a/docs/tutorials/pytorch2onnx.md
+++ b/docs/tutorials/pytorch2onnx.md
@@ -131,67 +131,67 @@ python tools/deployment/test.py \
 
 ### Results and Models
 
-<table>
+<table border="1" class="docutils">
 	<tr>
-	    <th>Model</th>
-	    <th>Config</th>
-	    <th>Metric</th>
-	    <th>PyTorch</th>
-	    <th>ONNX Runtime</th>
+	    <th align="center">Model</th>
+	    <th align="center">Config</th>
+	    <th align="center">Metric</th>
+	    <th align="center">PyTorch</th>
+	    <th align="center">ONNX Runtime</th>
 	</tr >
   <tr >
-	    <td>FCOS</td>
-	    <td>configs/fcos/fcos_r50_caffe_fpn_gn-head_4x4_1x_coco.py</td>
-	    <td>Box AP</td>
-	    <td>36.6</td>
-	    <td>36.5</td>
+	    <td align="center">FCOS</td>
+	    <td align="center"><code>configs/fcos/fcos_r50_caffe_fpn_gn-head_4x4_1x_coco.py</code></td>
+	    <td align="center">Box AP</td>
+	    <td align="center">36.6</td>
+	    <td align="center">36.5</td>
 	</tr>
   <tr >
-	    <td>FSAF</td>
-	    <td>configs/fsaf/fsaf_r50_fpn_1x_coco.py</td>
-	    <td>Box AP</td>
-	    <td>36.0</td>
-	    <td>36.0</td>
+	    <td align="center">FSAF</td>
+	    <td align="center"><code>configs/fsaf/fsaf_r50_fpn_1x_coco.py</code></td>
+	    <td align="center">Box AP</td>
+	    <td align="center">36.0</td>
+	    <td align="center">36.0</td>
 	</tr>
   <tr >
-	    <td>RetinaNet</td>
-	    <td>configs/retinanet/retinanet_r50_fpn_1x_coco.py</td>
-	    <td>Box AP</td>
-	    <td>36.5</td>
-	    <td>36.4</td>
+	    <td align="center">RetinaNet</td>
+	    <td align="center"><code>configs/retinanet/retinanet_r50_fpn_1x_coco.py</code></td>
+	    <td align="center">Box AP</td>
+	    <td align="center">36.5</td>
+	    <td align="center">36.4</td>
 	</tr>
 	<tr >
-	    <td >SSD</td>
-	    <td>configs/ssd/ssd300_coco.py</td>
-	    <td>Box AP</td>
-	    <td>25.6</td>
-	    <td>25.6</td>
+	    <td align="center" align="center" >SSD</td>
+	    <td align="center" align="center"><code>configs/ssd/ssd300_coco.py</code></td>
+	    <td align="center" align="center">Box AP</td>
+	    <td align="center" align="center">25.6</td>
+	    <td align="center" align="center">25.6</td>
 	</tr>
   <tr >
-	    <td>YOLOv3</td>
-	    <td>configs/yolo/yolov3_d53_mstrain-608_273e_coco.py</td>
-	    <td>Box AP</td>
-	    <td>33.5</td>
-	    <td>33.5</td>
+	    <td align="center">YOLOv3</td>
+	    <td align="center"><code>configs/yolo/yolov3_d53_mstrain-608_273e_coco.py</code></td>
+	    <td align="center">Box AP</td>
+	    <td align="center">33.5</td>
+	    <td align="center">33.5</td>
 	</tr>
   <tr >
-	    <td>Faster R-CNN</td>
-	    <td>configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py</td>
-	    <td>Box AP</td>
-	    <td>37.4</td>
-	    <td>37.4</td>
+	    <td align="center">Faster R-CNN</td>
+	    <td align="center"><code>configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py</code></td>
+	    <td align="center">Box AP</td>
+	    <td align="center">37.4</td>
+	    <td align="center">37.4</td>
 	</tr>
   <tr >
-	    <td rowspan="2">Mask R-CNN</td>
-	    <td rowspan="2">configs/mask_rcnn/mask_rcnn_r50_fpn_1x_coco.py</td>
-	    <td>Box AP</td>
-	    <td>38.2</td>
-	    <td>38.1</td>
+	    <td align="center" rowspan="2">Mask R-CNN</td>
+	    <td align="center" rowspan="2"><code>configs/mask_rcnn/mask_rcnn_r50_fpn_1x_coco.py</code></td>
+	    <td align="center">Box AP</td>
+	    <td align="center">38.2</td>
+	    <td align="center">38.1</td>
 	</tr>
 	<tr>
-	    <td>Mask AP</td>
-	    <td>34.7</td>
-	    <td>33.7</td>
+	    <td align="center">Mask AP</td>
+	    <td align="center">34.7</td>
+	    <td align="center">33.7</td>
 	</tr>
 </table>
 
diff --git a/mmdet/models/builder.py b/mmdet/models/builder.py
index b3d0777571f..85dc2562da1 100644
--- a/mmdet/models/builder.py
+++ b/mmdet/models/builder.py
@@ -1,67 +1,47 @@
 import warnings
 
-from mmcv.runner import Sequential
-from mmcv.utils import Registry, build_from_cfg
-
-BACKBONES = Registry('backbone')
-NECKS = Registry('neck')
-ROI_EXTRACTORS = Registry('roi_extractor')
-SHARED_HEADS = Registry('shared_head')
-HEADS = Registry('head')
-LOSSES = Registry('loss')
-DETECTORS = Registry('detector')
-
-
-def build(cfg, registry, default_args=None):
-    """Build a module.
-
-    Args:
-        cfg (dict, list[dict]): The config of modules, is is either a dict
-            or a list of configs.
-        registry (:obj:`Registry`): A registry the module belongs to.
-        default_args (dict, optional): Default arguments to build the module.
-            Defaults to None.
-
-    Returns:
-        nn.Module: A built nn module.
-    """
-    if isinstance(cfg, list):
-        modules = [
-            build_from_cfg(cfg_, registry, default_args) for cfg_ in cfg
-        ]
-        return Sequential(*modules)
-    else:
-        return build_from_cfg(cfg, registry, default_args)
+from mmcv.cnn import MODELS as MMCV_MODELS
+from mmcv.utils import Registry
+
+MODELS = Registry('models', parent=MMCV_MODELS)
+
+BACKBONES = MODELS
+NECKS = MODELS
+ROI_EXTRACTORS = MODELS
+SHARED_HEADS = MODELS
+HEADS = MODELS
+LOSSES = MODELS
+DETECTORS = MODELS
 
 
 def build_backbone(cfg):
     """Build backbone."""
-    return build(cfg, BACKBONES)
+    return BACKBONES.build(cfg)
 
 
 def build_neck(cfg):
     """Build neck."""
-    return build(cfg, NECKS)
+    return NECKS.build(cfg)
 
 
 def build_roi_extractor(cfg):
     """Build roi extractor."""
-    return build(cfg, ROI_EXTRACTORS)
+    return ROI_EXTRACTORS.build(cfg)
 
 
 def build_shared_head(cfg):
     """Build shared head."""
-    return build(cfg, SHARED_HEADS)
+    return SHARED_HEADS.build(cfg)
 
 
 def build_head(cfg):
     """Build head."""
-    return build(cfg, HEADS)
+    return HEADS.build(cfg)
 
 
 def build_loss(cfg):
     """Build loss."""
-    return build(cfg, LOSSES)
+    return LOSSES.build(cfg)
 
 
 def build_detector(cfg, train_cfg=None, test_cfg=None):
@@ -74,4 +54,5 @@ def build_detector(cfg, train_cfg=None, test_cfg=None):
         'train_cfg specified in both outer field and model field '
     assert cfg.get('test_cfg') is None or test_cfg is None, \
         'test_cfg specified in both outer field and model field '
-    return build(cfg, DETECTORS, dict(train_cfg=train_cfg, test_cfg=test_cfg))
+    return DETECTORS.build(
+        cfg, default_args=dict(train_cfg=train_cfg, test_cfg=test_cfg))
diff --git a/mmdet/models/roi_heads/test_mixins.py b/mmdet/models/roi_heads/test_mixins.py
index a47d46ce913..d4505a0e7cc 100644
--- a/mmdet/models/roi_heads/test_mixins.py
+++ b/mmdet/models/roi_heads/test_mixins.py
@@ -114,8 +114,8 @@ def simple_test_bboxes(self,
         cls_score = cls_score.reshape(batch_size, num_proposals_per_img, -1)
 
         if not torch.onnx.is_in_onnx_export():
-            # remove padding
-            supplement_mask = rois[..., -1] == 0
+            # remove padding, ignore batch_index when calculating mask
+            supplement_mask = rois.abs()[..., 1:].sum(dim=-1) == 0
             cls_score[supplement_mask, :] = 0
 
         # bbox_pred would be None in some detector when with_reg is False,
@@ -137,7 +137,7 @@ def simple_test_bboxes(self,
                 det_labels = []
                 for i in range(len(proposals)):
                     # remove padding
-                    supplement_mask = proposals[i][..., -1] == 0
+                    supplement_mask = proposals[i].abs().sum(dim=-1) == 0
                     for bbox in bbox_preds[i]:
                         bbox[supplement_mask] = 0
                     det_bbox, det_label = self.bbox_head.get_bboxes(
@@ -320,7 +320,7 @@ def simple_test_mask(self,
             det_label = det_labels[i]
 
             # remove padding
-            supplement_mask = det_bbox[..., -1] != 0
+            supplement_mask = det_bbox.abs().sum(dim=-1) != 0
             mask_pred = mask_pred[supplement_mask]
             det_bbox = det_bbox[supplement_mask]
             det_label = det_label[supplement_mask]