diff --git a/dygraph/ppdet/engine/trainer.py b/dygraph/ppdet/engine/trainer.py
index d18492a4ebabd59982606ef3e63b7e48e3e6bd94..771866f65e0fe738f247db4d0e3dd07ce3a7126c 100644
--- a/dygraph/ppdet/engine/trainer.py
+++ b/dygraph/ppdet/engine/trainer.py
@@ -115,9 +115,10 @@ class Trainer(object):
             return
         if self.cfg.metric == 'COCO':
             # TODO: bias should be unified
+            bias = 1 if 'bias' in self.cfg else 0
             self._metrics = [
                 COCOMetric(
-                    anno_file=self.dataset.get_anno(), bias=self.cfg.bias)
+                    anno_file=self.dataset.get_anno(), bias=bias)
             ]
         elif self.cfg.metric == 'VOC':
             self._metrics = [