To simplify and automate the verification of composite Web services,a method based on extended deterministic finite automata(EDFA) is presented.EDFA can describe Web services in an accurate way:the nodes represent states maintained by a service during the interactions between the service and its clients;the state transitions represent message exchanges between the service and its clients.Therefore,the automaton depicts the temporal sequences of messages,i.e.the behavior of the service.With the EDFA-based method for the verification of composite Web services,whether the capabilities of a service meet system requirements and whether there exist logic errors in the interactions between a service and its clients can be verified.Compared with other methods,this method is more suitable for the verification of composite Web services in an open environment.