diff --git a/swift/llm/infer/infer_engine/vllm_engine.py b/swift/llm/infer/infer_engine/vllm_engine.py
index c6dcaad132..4cda410455 100644
--- a/swift/llm/infer/infer_engine/vllm_engine.py
+++ b/swift/llm/infer/infer_engine/vllm_engine.py
@@ -167,10 +167,20 @@ def _load_generation_config(self) -> None:
             max_new_tokens = kwargs.get('max_new_tokens')
             if max_new_tokens is not None:
                 kwargs['max_tokens'] = max_new_tokens
-            parameters = inspect.signature(SamplingParams.__init__).parameters
+            parameters = inspect.signature(SamplingParams).parameters
             for k, v in kwargs.copy().items():
                 if k not in parameters or v is None:
                     kwargs.pop(k)
+                    continue
+                # Check if parameter class has from_optional method
+                param_type = parameters[k].annotation
+                
+                if str(param_type).startswith('typing.Optional'):
+                    # Extract the actual type from Optional
+                    param_type = param_type.__args__[0]
+                if hasattr(param_type, 'from_optional') and v is not None:
+                    kwargs[k] = param_type.from_optional(v)
+                    
             self.generation_config = SamplingParams(**kwargs)
         else:
             self.generation_config = SamplingParams()
@@ -246,18 +256,18 @@ def _get_logprobs(tokenizer: PreTrainedTokenizerBase,
         return {'content': res}
 
     def _prepare_generation_config(self, request_config: RequestConfig) -> SamplingParams:
-        kwargs = {'max_tokens': request_config.max_tokens}
-        for key in ['temperature', 'top_k', 'top_p', 'repetition_penalty']:
+        import msgspec
+        kwargs = msgspec.structs.asdict(self.generation_config)
+        
+        for key in ['max_tokens', 'temperature', 'top_k', 'top_p', 'repetition_penalty']:
             new_value = getattr(request_config, key)
-            if new_value is None:
-                kwargs[key] = getattr(self.generation_config, key)
-            else:
+            if new_value:
                 kwargs[key] = new_value
 
         if request_config.logprobs:
-            kwargs['logprobs'] = 1
-            if request_config.top_logprobs is not None:
-                kwargs['logprobs'] = max(1, request_config.top_logprobs)
+            top_logprobs = request_config.top_logprobs or 1
+            kwargs['logprobs'] = max(1, top_logprobs)
+
 
         # TODO: beam search
         for key in ['n', 'best_of', 'frequency_penalty', 'presence_penalty', 'seed']: