diff --git a/data_juicer/format/mixture_formatter.py b/data_juicer/format/mixture_formatter.py
index f55907f90..d8cc6b9ad 100644
--- a/data_juicer/format/mixture_formatter.py
+++ b/data_juicer/format/mixture_formatter.py
@@ -17,6 +17,7 @@ def __init__(self,
                  suffixes: Union[str, List[str], Tuple[str]] = None,
                  text_keys=None,
                  add_suffix=False,
+                 max_samples=None,
                  **kwargs):
         """
         Initialization method.
@@ -28,9 +29,30 @@ def __init__(self,
         :param text_keys: key names of field that stores sample text.
         :param add_suffix: whether to add the file suffix to dataset
             meta info
+        :param max_samples: max samples number of mixed dataset.
         :param kwargs: extra args
         """
+
         data_prefixes, weights = self._get_weight(data_prefix=dataset_path)
+        sample_numbers = [0] * len(weights)
+        if max_samples is not None:
+            # Normalize weights.
+            weights = np.array(weights, dtype=np.float64)
+            sum_weights = np.sum(weights)
+            assert sum_weights > 0.0
+            weights /= sum_weights
+            sample_num_per_dataset = [
+                int(np.ceil(max_samples * weight)) for weight in weights
+            ]
+
+            # Adjust
+            acc_sample_numbers = 0
+            for i in range(len(sample_num_per_dataset)):
+                sample_numbers[i] = min(sample_num_per_dataset[i],
+                                        max_samples - acc_sample_numbers)
+                acc_sample_numbers += sample_numbers[i]
+
+        self.sample_numbers = sample_numbers
         self.weights = weights
         self.formatters = [
             load_formatter(dataset_path=data_prefix,
@@ -65,21 +87,38 @@ def _get_weight(self, data_prefix):
                 prefixes.append(value)
         return prefixes, weights
 
-    def _random_sample(self, dataset, weight=1.0, seed=None):
+    def _random_sample(self, dataset, weight=1.0, sample_number=0, seed=None):
         """
-        Randomly sample a subset from a dataset with weight.
+        Randomly sample a subset from a dataset with weight or number,
+        if sample number is bigger than 0, we will use sample
+        number instead of weight.
         :param dataset: a HuggingFace dataset
         :param weight: sample ratio of dataset
+        :param sample_number: sample number of dataset
         :param seed: random sample seed, if None, 42 as default
         :return: a subset of dataset
         """
         if seed is None:
             seed = 42
-        num_samples = min(int(np.ceil(dataset.num_rows * weight)),
-                          dataset.num_rows)
-        if num_samples == dataset.num_rows:
+
+        ds_samples = dataset.num_rows
+        if sample_number <= 0:
+            sample_number = int(np.ceil(ds_samples * weight))
+
+        if sample_number == ds_samples:
             return dataset
-        return dataset.shuffle(seed=seed).select(range(num_samples))
+
+        num_epochs = int(np.ceil(sample_number / ds_samples)) - 1
+
+        if num_epochs > 0:
+            remain_samples = sample_number - num_epochs * ds_samples
+            sample_index = list(range(ds_samples)) * num_epochs + list(
+                range(remain_samples))
+        else:
+            remain_samples = sample_number
+            sample_index = list(range(remain_samples))
+
+        return dataset.shuffle(seed=seed).select(sample_index)
 
     def load_dataset(self, num_proc: int = 1, global_cfg=None) -> Dataset:
         """
@@ -90,11 +129,13 @@ def load_dataset(self, num_proc: int = 1, global_cfg=None) -> Dataset:
         :return: mixed dataset
         """
         dataset_list = []
-        for weight, formatter in zip(self.weights, self.formatters):
+        for weight, sample_num, formatter in zip(self.weights,
+                                                 self.sample_numbers,
+                                                 self.formatters):
             dataset = formatter.load_dataset(num_proc, global_cfg)
-            sampled = self._random_sample(dataset, weight)
+            sampled = self._random_sample(dataset, weight, sample_num)
             logger.info(f'sampled {len(sampled)} from '
-                        f'{len(dataset)} with weight {weight}')
+                        f'{len(dataset)}')
             dataset_list.append(sampled)
 
         from data_juicer.core.data import NestedDataset
diff --git a/tools/postprocess/data_mixture.py b/tools/postprocess/data_mixture.py
index 146986976..db89a2a1f 100644
--- a/tools/postprocess/data_mixture.py
+++ b/tools/postprocess/data_mixture.py
@@ -33,6 +33,11 @@ def parse_args():
                         'size of each shard won\'t larger than the '
                         'export_shard_size')
 
+    parser.add_argument('--max_samples',
+                        type=int,
+                        default=None,
+                        help='Number of samples of mixed dataset.')
+
     parser.add_argument('--num_proc',
                         type=int,
                         default=4,
@@ -58,7 +63,7 @@ def run_mixture():
     """
     args = parse_args()
     data_path = ' '.join(args.data_path)
-    formatter = load_formatter(data_path)
+    formatter = load_formatter(data_path, max_samples=args.max_samples)
     dataset = formatter.load_dataset(args.num_proc)
     exporter = Exporter(export_path=args.export_path,
                         export_shard_size=args.export_shard_size,