diff --git a/PaddleCV/rcnn/eval_coco_map.py b/PaddleCV/rcnn/eval_coco_map.py
index 019bd877f244df5b3647cd3f227298b61842bf94..b0439fa053d869abc3d4da9d3622013308a522a5 100644
--- a/PaddleCV/rcnn/eval_coco_map.py
+++ b/PaddleCV/rcnn/eval_coco_map.py
@@ -17,6 +17,7 @@ from __future__ import division
 from __future__ import print_function
 import os
 import io
+import six
 import time
 import numpy as np
 from eval_helper import *
@@ -118,7 +119,8 @@ def eval():
             Please use reasonable model and check input data."
 
     with io.open("detection_bbox_result.json", 'w') as outfile:
-        outfile.write(unicode(json.dumps(dts_res)))
+        encode_func = unicode if six.PY2 else str
+        outfile.write(encode_func(json.dumps(dts_res)))
     print("start evaluate bbox using coco api")
     cocoDt = cocoGt.loadRes("detection_bbox_result.json")
     cocoEval = COCOeval(cocoGt, cocoDt, 'bbox')
@@ -128,7 +130,8 @@ def eval():
 
     if cfg.MASK_ON:
         with io.open("detection_segms_result.json", 'w') as outfile:
-            outfile.write(unicode(json.dumps(segms_res)))
+            encode_func = unicode if six.PY2 else str
+            outfile.write(encode_func(json.dumps(segms_res)))
         print("start evaluate mask using coco api")
         cocoDt = cocoGt.loadRes("detection_segms_result.json")
         cocoEval = COCOeval(cocoGt, cocoDt, 'segm')
diff --git a/PaddleCV/ssd/eval_coco_map.py b/PaddleCV/ssd/eval_coco_map.py
index e43391de49dd747aa488f73dd2255691622540cc..c008430776e33ccfaea910b39776292783630eb2 100644
--- a/PaddleCV/ssd/eval_coco_map.py
+++ b/PaddleCV/ssd/eval_coco_map.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 import os
 import io
+import six
 import time
 import numpy as np
 import argparse
@@ -130,7 +131,8 @@ def eval(args, data_args, test_list, batch_size, model_dir=None):
             dts_res += get_dt_res(nmsed_out_v, data)
 
         with io.open("detection_result.json", 'w') as outfile:
-            outfile.write(unicode(json.dumps(dts_res)))
+            encode_func = unicode if six.PY2 else str
+            outfile.write(encode_func(json.dumps(dts_res)))
         print("start evaluate using coco api")
         cocoGt = COCO(os.path.join(data_args.data_dir, test_list))
         cocoDt = cocoGt.loadRes("detection_result.json")
diff --git a/PaddleCV/yolov3/eval.py b/PaddleCV/yolov3/eval.py
index e2b2bc559ae5092109bf1cb26e3e48dac1cf2583..3443ccfcbff186e2db51ce795bb1569160c81ddb 100644
--- a/PaddleCV/yolov3/eval.py
+++ b/PaddleCV/yolov3/eval.py
@@ -17,6 +17,7 @@ from __future__ import division
 from __future__ import print_function
 import os
 import io
+import six
 import time
 import json
 import numpy as np
@@ -115,7 +116,8 @@ def eval():
         total_time += end_time - start_time
 
     with io.open("yolov3_result.json", 'w') as outfile:
-        outfile.write(unicode(json.dumps(dts_res)))
+        encode_func = unicode if six.PY2 else str
+        outfile.write(encode_func(json.dumps(dts_res)))
     print("start evaluate detection result with coco api")
     coco = COCO(os.path.join(cfg.data_dir, test_list))
     cocoDt = coco.loadRes("yolov3_result.json")