diff --git a/paddle/fluid/operators/roi_align_op.cc b/paddle/fluid/operators/roi_align_op.cc
index 12d83f2e51721e09c2478760c125bbeed7459d7e..2287b2146016cc29af2346375ff6515174587898 100644
--- a/paddle/fluid/operators/roi_align_op.cc
+++ b/paddle/fluid/operators/roi_align_op.cc
@@ -132,7 +132,20 @@ class ROIAlignOpMaker : public framework::OpProtoAndCheckerMaker {
                  "and pooled_w, likewise for height")
         .SetDefault(-1);
     AddComment(R"DOC(
-    
+**RoIAlign Operator**
+
+Region of interest align (also known as RoI align) is to perform
+bilinear interpolation on inputs of nonuniform sizes to obtain 
+fixed-size feature maps (e.g. 7*7)
+
+Dividing each region proposal into equal-sized sections with
+the pooled_width and pooled_height. Location remains the origin
+result.
+
+In each ROI bin, the value of the four regularly sampled locations 
+are computed directly through bilinear interpolation. The output is
+the mean of four locations.
+Thus avoid the misaligned problem.   
     )DOC");
   }
 };
diff --git a/python/paddle/fluid/tests/unittests/test_roi_align_op.py b/python/paddle/fluid/tests/unittests/test_roi_align_op.py
index 1028d38759bddf7c0f5337f3a2fc3c87e9a48c32..1a252ea547e4d93d83f64fa9cdb3605eeef0a3cf 100644
--- a/python/paddle/fluid/tests/unittests/test_roi_align_op.py
+++ b/python/paddle/fluid/tests/unittests/test_roi_align_op.py
@@ -167,4 +167,4 @@ class TestROIAlignOp(OpTest):
         self.check_output()
 
     def test_check_grad(self):
-        self.check_grad(['X'], 'Out', max_relative_error=0.005)
+        self.check_grad(['X'], 'Out')