diff --git a/fastdeploy/engine/common_engine_prepare_mixin.py b/fastdeploy/engine/common_engine_prepare_mixin.py
index c6ea2f3ee9d..4129dfec664 100644
--- a/fastdeploy/engine/common_engine_prepare_mixin.py
+++ b/fastdeploy/engine/common_engine_prepare_mixin.py
@@ -89,9 +89,15 @@ def _fetch_request_decode(self) -> bool:
 
     def _fetch_request_prefill(self) -> bool:
         """Fetch and prepare requests for a prefill instance. Returns True if tasks were fetched."""
+        max_inflight_prefill = envs.FD_MAX_INFLIGHT_PREFILL
+        inflight_prefill = len(self.resource_manager.running)
+        if inflight_prefill >= max_inflight_prefill:
+            return False
+        available_for_new = max_inflight_prefill - inflight_prefill
         num_prefill_batch = min(
             int(self.resource_manager.available_batch()),
             self.cfg.max_prefill_batch,
+            available_for_new,
         )
         max_num_batched_tokens = self.cfg.scheduler_config.max_num_batched_tokens
         available_blocks = self.cfg.cache_config.max_block_num_per_seq
diff --git a/fastdeploy/envs.py b/fastdeploy/envs.py
index 61b6b1e31d1..0979159f339 100644
--- a/fastdeploy/envs.py
+++ b/fastdeploy/envs.py
@@ -196,6 +196,7 @@ def _validate_split_kv_size(value: int) -> int:
     # Number of worker threads for prepare requests in prefill instance
     "FD_PREFILL_PREPARE_REQ_THREAD_NUM": lambda: int(os.getenv("FD_PREFILL_PREPARE_REQ_THREAD_NUM", "3")),
     "FD_PREFILL_WAIT_DECODE_RESOURCE_SECONDS": lambda: int(os.getenv("FD_PREFILL_WAIT_DECODE_RESOURCE_SECONDS", "30")),
+    "FD_MAX_INFLIGHT_PREFILL": lambda: int(os.getenv("FD_MAX_INFLIGHT_PREFILL", "20")),
     # Timeout (seconds) for D to reclaim preallocated blocks if P never follows through. 0 to disable.
     "FD_DECODE_PREALLOC_BLOCK_TIMEOUT": lambda: int(os.getenv("FD_DECODE_PREALLOC_BLOCK_TIMEOUT", "1200")),
     "FD_ENABLE_REQUEST_DISCONNECT_STOP_INFERENCE": lambda: int(