diff --git a/mmpose/datasets/dataset_wrappers.py b/mmpose/datasets/dataset_wrappers.py
index aaaa173b91..cdbe73d227 100644
--- a/mmpose/datasets/dataset_wrappers.py
+++ b/mmpose/datasets/dataset_wrappers.py
@@ -1,7 +1,116 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+import numpy as np
+from mmcv.utils import print_log
+from torch.utils.data.dataset import ConcatDataset as _ConcatDataset
+
 from .builder import DATASETS
 
 
+@DATASETS.register_module()
+class ConcatDataset(_ConcatDataset):
+    """A wrapper of concatenated dataset.
+
+    Same as :obj:`torch.utils.data.dataset.ConcatDataset`, but
+    concat the group flag for image aspect ratio.
+
+    Args:
+        datasets (list[:obj:`Dataset`]): A list of datasets.
+        separate_eval (bool): Whether to evaluate the results
+            separately if it is used as validation dataset.
+            Defaults to True.
+    """
+
+    def __init__(self, datasets, separate_eval=True):
+        super(ConcatDataset, self).__init__(datasets)
+        self.separate_eval = separate_eval
+
+    def clip_by_index(self, results, start_idx, end_idx):
+        clip_res = dict()
+        clip_res['preds'] = results[0]['preds'][start_idx:end_idx, :, :]
+        clip_res['boxes'] = results[0]['boxes'][start_idx:end_idx, :]
+        clip_res['image_paths'] = results[0]['image_paths'][start_idx:end_idx]
+        clip_res['bbox_ids'] = results[0]['bbox_ids'][start_idx:end_idx]
+        return [clip_res]
+
+    def rebuild_results(self, results):
+        new_results = list()
+        new_res = results[0]
+        new_results.append(new_res)
+        for i in range(1, len(results)):
+            res = results[i]
+            new_res['preds'] = np.append(new_res['preds'], res['preds'], axis=0)
+            new_res['boxes'] = np.append(new_res['boxes'], res['boxes'], axis=0)
+            new_res['image_paths'] += res['image_paths']
+            new_res['bbox_ids'] += res['bbox_ids']
+        return new_results, len(new_res['image_paths'])
+
+    def update_total_eval_results_ap(self, eval_ap_list, total_eval_results):
+        sum_num = 0
+        sum_precision = 0
+        for eval_ap in eval_ap_list:
+            numbers = eval_ap['numbers']
+            precisions = numbers * eval_ap['AP']
+            sum_num += numbers
+            sum_precision += precisions
+        total_eval_results.update({'AP': sum_precision/sum_num})
+
+
+    def evaluate(self, results, logger=None, **kwargs):
+        """Evaluate the results.
+
+        Args:
+            results (list[list | tuple]): Testing results of the dataset.
+            logger (logging.Logger | str | None): Logger used for printing
+                related information during evaluation. Default: None.
+
+        Returns:
+            dict[str: float]: AP results of the total dataset or each separate
+            dataset if `self.separate_eval=True`.
+        """
+
+        new_results, res_len = self.rebuild_results(results)
+        assert res_len == self.cumulative_sizes[-1], \
+            ('Dataset and results have different sizes: '
+             f'{self.cumulative_sizes[-1]} v.s. {len(results)}')
+
+        # Check whether all the datasets support evaluation
+        for dataset in self.datasets:
+            assert hasattr(dataset, 'evaluate'), \
+                f'{type(dataset)} does not implement evaluate function'
+
+        if self.separate_eval:
+            total_eval_results = dict()
+            eval_ap_list = list()
+            for dataset_idx, dataset in enumerate(self.datasets):
+                start_idx = 0 if dataset_idx == 0 else \
+                    self.cumulative_sizes[dataset_idx - 1]
+                end_idx = self.cumulative_sizes[dataset_idx]
+
+                results_per_dataset = self.clip_by_index(new_results, start_idx, end_idx)
+                print_log(
+                    f'Evaluateing dataset-{dataset_idx} with '
+                    f'{len(results_per_dataset)} images now',
+                    logger=logger)
+
+                eval_results_per_dataset = dataset.evaluate(
+                    results_per_dataset, logger=logger, **kwargs)
+                for k, v in eval_results_per_dataset.items():
+                    total_eval_results.update({f'{dataset_idx}_{k}': v})
+
+                if 'AP' in eval_results_per_dataset.keys():
+                    eval_ap_list.append(dict(numbers=end_idx-start_idx, AP=eval_results_per_dataset['AP']))
+
+            if len(eval_ap_list) > 0:
+                self.update_total_eval_results_ap(eval_ap_list, total_eval_results)
+            return total_eval_results
+        elif len(set([type(ds) for ds in self.datasets])) != 1:
+            raise NotImplementedError(
+                'All the datasets should have same types')
+        else:
+            raise NotImplementedError(
+                'separate_eval=False not implemented')
+
+
 @DATASETS.register_module()
 class RepeatDataset:
     """A wrapper of repeated dataset.