diff --git a/python/sglang/multimodal_gen/configs/sample/sampling_params.py b/python/sglang/multimodal_gen/configs/sample/sampling_params.py
index fd00f82dc..ec387da2d 100644
--- a/python/sglang/multimodal_gen/configs/sample/sampling_params.py
+++ b/python/sglang/multimodal_gen/configs/sample/sampling_params.py
@@ -624,8 +624,9 @@ class SamplingParams:
         parser.add_argument(
             "--prompt",
             type=str,
+            nargs="+",
             default=SamplingParams.prompt,
-            help="Text prompt for generation",
+            help="Text prompt(s) for generation. Use space-separated values for multiple prompts, e.g., --prompt 'prompt 1' 'prompt 2'",
         )
         parser.add_argument(
             "--negative-prompt",
diff --git a/python/sglang/multimodal_gen/runtime/entrypoints/diffusion_generator.py b/python/sglang/multimodal_gen/runtime/entrypoints/diffusion_generator.py
index 12631f137..162df5f89 100644
--- a/python/sglang/multimodal_gen/runtime/entrypoints/diffusion_generator.py
+++ b/python/sglang/multimodal_gen/runtime/entrypoints/diffusion_generator.py
@@ -166,12 +166,19 @@ class DiffGenerator:
         """
         # 1. prepare requests
         prompts = self._resolve_prompts(sampling_params_kwargs.get("prompt"))
+        user_output_file_name = sampling_params_kwargs.get("output_file_name")
+
+        if len(prompts) > 1 and user_output_file_name is not None:
+            raise ValueError(
+                "Cannot use multiple prompts with a fixed output_file_name. "
+                "Either remove --output-file-name or use a single prompt."
+            )
+
         sampling_params_orig = SamplingParams.from_user_sampling_params_args(
             self.server_args.model_path,
             server_args=self.server_args,
             **sampling_params_kwargs,
         )
-        user_output_file_name = sampling_params_kwargs.get("output_file_name")
 
         requests: list[Req] = []
         for p in prompts: