diff --git a/dygraph/ppdet/engine/trainer.py b/dygraph/ppdet/engine/trainer.py
index 771866f65e0fe738f247db4d0e3dd07ce3a7126c..4e58d88944c70a69294c1208c0b3717675c66e70 100644
--- a/dygraph/ppdet/engine/trainer.py
+++ b/dygraph/ppdet/engine/trainer.py
@@ -115,7 +115,7 @@ class Trainer(object):
             return
         if self.cfg.metric == 'COCO':
             # TODO: bias should be unified
-            bias = 1 if 'bias' in self.cfg else 0
+            bias = self.cfg['bias'] if 'bias' in self.cfg else 0
             self._metrics = [
                 COCOMetric(
                     anno_file=self.dataset.get_anno(), bias=bias)