diff --git a/python/sglang/srt/layers/attention/trtllm_mha_backend.py b/python/sglang/srt/layers/attention/trtllm_mha_backend.py
index 728094dec..aa418b7af 100644
--- a/python/sglang/srt/layers/attention/trtllm_mha_backend.py
+++ b/python/sglang/srt/layers/attention/trtllm_mha_backend.py
@@ -11,6 +11,7 @@ from typing import TYPE_CHECKING, Optional
 
 import torch
 
+from sglang.srt.environ import envs
 from sglang.srt.layers.attention.flashinfer_backend import (
     FlashInferAttnBackend,
     FlashInferMultiStepDraftBackend,
@@ -32,9 +33,9 @@ if TYPE_CHECKING:
     from sglang.srt.speculative.spec_info import SpecInput
 
 # Constants
-DEFAULT_WORKSPACE_SIZE_MB = (
-    512  # Memory workspace size in MB, todo(Yingyi): read from config
-)
+# Default workspace size in MB for TRTLLM MHA
+# Can be configured via SGLANG_FLASHINFER_WORKSPACE_SIZE environment variable
+DEFAULT_WORKSPACE_SIZE_MB = 512
 
 # Reuse this workspace buffer across all TRTLLM MHA wrappers
 global_zero_init_workspace_buffer = None
@@ -67,6 +68,15 @@ class TRTLLMHAAttnBackend(FlashInferAttnBackend):
         kv_last_page_len_buf: Optional[torch.Tensor] = None,
         speculative_step_id: int = 0,
     ):
+        # Capture workspace size before super().__init__() to preserve user's
+        # SGLANG_FLASHINFER_WORKSPACE_SIZE setting (may be overridden by parent)
+        env_var = envs.SGLANG_FLASHINFER_WORKSPACE_SIZE
+        workspace_size_bytes = (
+            env_var.get()
+            if env_var.is_set()
+            else DEFAULT_WORKSPACE_SIZE_MB * 1024 * 1024
+        )
+
         super().__init__(
             model_runner, skip_prefill, kv_indptr_buf, kv_last_page_len_buf
         )
@@ -85,7 +95,7 @@ class TRTLLMHAAttnBackend(FlashInferAttnBackend):
         self.device = model_runner.device
 
         # Workspace allocation
-        self.workspace_size = DEFAULT_WORKSPACE_SIZE_MB * 1024 * 1024
+        self.workspace_size = workspace_size_bytes
         # Allocate buffers
         global global_zero_init_workspace_buffer
         if global_zero_init_workspace_buffer is None: