Web service technology is being applied to organizing business process in many large-scale enterprises. Discovery of composite service, therefore, has become an active research area. In this paper, we utilize a PLWAP-tree algorithm to analyze the relationship among web services from web service usage log. This method generates time-ordered sets of web services which can be exploited to integrate into a real business process. The empirical result shows the methodology is useful, flexible, and efficient. It is able to integrate web services into a composite service according to the mining result.