diff --git a/tools/misc/split_coco.py b/tools/misc/split_coco.py
new file mode 100644
index 000000000..78cc65503
--- /dev/null
+++ b/tools/misc/split_coco.py
@@ -0,0 +1,109 @@
+# Copyright (c) OpenMMLab. All rights reserved.
+import argparse
+import os.path as osp
+
+import mmcv
+import numpy as np
+
+prog_description = '''K-Fold coco split.
+
+To split coco data for semi-supervised object detection:
+    python tools/misc/split_coco.py
+'''
+
+
+def parse_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        '--data-root',
+        type=str,
+        help='The data root of coco dataset.',
+        default='./data/coco/')
+    parser.add_argument(
+        '--out-dir',
+        type=str,
+        help='The output directory of coco semi-supervised annotations.',
+        default='./data/coco_semi_annos/')
+    parser.add_argument(
+        '--labeled-percent',
+        type=float,
+        nargs='+',
+        help='The percentage of labeled data in the training set.',
+        default=[1, 2, 5, 10])
+    parser.add_argument(
+        '--fold',
+        type=int,
+        help='K-fold cross validation for semi-supervised object detection.',
+        default=5)
+    args = parser.parse_args()
+    return args
+
+
+def split_coco(data_root, out_dir, percent, fold):
+    """Split COCO data for Semi-supervised object detection.
+
+    Args:
+        data_root (str): The data root of coco dataset.
+        out_dir (str): The output directory of coco semi-supervised
+            annotations.
+        percent (float): The percentage of labeled data in the training set.
+        fold (int): The fold of dataset and set as random seed for data split.
+    """
+
+    def save_anns(name, images, annotations):
+        sub_anns = dict()
+        sub_anns['images'] = images
+        sub_anns['annotations'] = annotations
+        sub_anns['licenses'] = anns['licenses']
+        sub_anns['categories'] = anns['categories']
+        sub_anns['info'] = anns['info']
+
+        mmcv.mkdir_or_exist(out_dir)
+        mmcv.dump(sub_anns, f'{out_dir}/{name}.json')
+
+    # set random seed with the fold
+    np.random.seed(fold)
+    ann_file = osp.join(data_root, 'annotations/instances_train2017.json')
+    anns = mmcv.load(ann_file)
+
+    image_list = anns['images']
+    labeled_total = int(percent / 100. * len(image_list))
+    labeled_inds = set(
+        np.random.choice(range(len(image_list)), size=labeled_total))
+    labeled_ids, labeled_images, unlabeled_images = [], [], []
+
+    for i in range(len(image_list)):
+        if i in labeled_inds:
+            labeled_images.append(image_list[i])
+            labeled_ids.append(image_list[i]['id'])
+        else:
+            unlabeled_images.append(image_list[i])
+
+    # get all annotations of labeled images
+    labeled_ids = set(labeled_ids)
+    labeled_annotations, unlabeled_annotations = [], []
+
+    for ann in anns['annotations']:
+        if ann['image_id'] in labeled_ids:
+            labeled_annotations.append(ann)
+        else:
+            unlabeled_annotations.append(ann)
+
+    # save labeled and unlabeled
+    labeled_name = f'instances_train2017.{fold}@{percent}'
+    unlabeled_name = f'instances_train2017.{fold}@{percent}-unlabeled'
+
+    save_anns(labeled_name, labeled_images, labeled_annotations)
+    save_anns(unlabeled_name, unlabeled_images, unlabeled_annotations)
+
+
+def multi_wrapper(args):
+    return split_coco(*args)
+
+
+if __name__ == '__main__':
+    args = parse_args()
+    arguments_list = [(args.data_root, args.out_dir, p, f)
+                      for f in range(1, args.fold + 1)
+                      for p in args.labeled_percent]
+    mmcv.track_parallel_progress(multi_wrapper, arguments_list, args.fold)