diff --git a/docs/user-guides/server.md b/docs/user-guides/server.md
index 49220f346..d7c113035 100644
--- a/docs/user-guides/server.md
+++ b/docs/user-guides/server.md
@@ -169,7 +169,6 @@ For PyTorch & ONNX backend, you can set the following parameters via `with`:
 | `name`    | Model weights, default is `ViT-B/32`. Support all OpenAI released pretrained models.                                           |
 | `num_worker_preprocess` | The number of CPU workers for image & text prerpocessing, default 4.                                                           | 
 | `minibatch_size` | The size of a minibatch for CPU preprocessing and GPU encoding, default 64. Reduce the size of it if you encounter OOM on GPU. |
-| `pool_backend` | The backend of the preprocessing worker pool, default is `thread`                                                               |
 
 There are also runtime-specific parameters listed below:
 
diff --git a/server/clip_server/executors/clip_onnx.py b/server/clip_server/executors/clip_onnx.py
index 3aa067a3d..1134e3237 100644
--- a/server/clip_server/executors/clip_onnx.py
+++ b/server/clip_server/executors/clip_onnx.py
@@ -29,7 +29,6 @@ def __init__(
         device: Optional[str] = None,
         num_worker_preprocess: int = 4,
         minibatch_size: int = 64,
-        pool_backend: str = 'thread',
         **kwargs,
     ):
         super().__init__(**kwargs)
@@ -37,10 +36,8 @@ def __init__(
 
         self._preprocess_blob = clip._transform_blob(_SIZE[name])
         self._preprocess_tensor = clip._transform_ndarray(_SIZE[name])
-        if pool_backend == 'thread':
-            self._pool = ThreadPool(processes=num_worker_preprocess)
-        else:
-            self._pool = Pool(processes=num_worker_preprocess)
+        self._pool = ThreadPool(processes=num_worker_preprocess)
+
         self._minibatch_size = minibatch_size
 
         self._model = CLIPOnnxModel(name)
diff --git a/server/clip_server/executors/clip_torch.py b/server/clip_server/executors/clip_torch.py
index 50ab7b82c..80d169905 100644
--- a/server/clip_server/executors/clip_torch.py
+++ b/server/clip_server/executors/clip_torch.py
@@ -1,6 +1,6 @@
 import os
 import numpy as np
-from multiprocessing.pool import ThreadPool, Pool
+from multiprocessing.pool import ThreadPool
 from typing import Optional, List, Tuple
 
 from jina import Executor, requests, DocumentArray
@@ -17,7 +17,6 @@ def __init__(
         jit: bool = False,
         num_worker_preprocess: int = 4,
         minibatch_size: int = 64,
-        pool_backend: str = 'thread',
         **kwargs,
     ):
         super().__init__(**kwargs)
@@ -51,10 +50,7 @@ def __init__(
             name, device=self._device, jit=jit
         )
 
-        if pool_backend == 'thread':
-            self._pool = ThreadPool(processes=num_worker_preprocess)
-        else:
-            self._pool = Pool(processes=num_worker_preprocess)
+        self._pool = ThreadPool(processes=num_worker_preprocess)
 
     def _preproc_image(self, da: 'DocumentArray') -> 'DocumentArray':
         for d in da: