To overcome the shortcoming of current web service composition modeling methods, a new web services composition process/resource model(WSCP/R-net) was proposed on the basis of the extended petri-net. WSCP/R-net resolves the problems on uncertain activity option and dynamic variation of service in process modeling effectively. Furthermore, a description of the methods to translate WSCP/R-net into BPEL4WS was made. Finally, its application was illustrated in city emergency disposal.