The use of web services becomes important. Since web services may be provided by unknown providers, many researchers designed mechanisms to ensure secure access of web services. Existing mechanisms generally statically decides whether a requester can invoke a web service but ignore the importance of dynamically preventing information leakage during web service execution. This paper proposes a latticebased information flow control model WSIFC (web service information flow control) to dynamically prevent information leakage. It uses simple rules to monitor the flows of sensitive information during web service execution.