Grid is a new paradigm of Internet computing to share distributed resources and collaborate among them. A web service-based approach for Grid can improve the extensibility and interoperability of Grid system. In this paper, a layered Grid functional model is discussed; within the OGSA (open grid service architecture) framework, a Web service-based Grid architecture is presented. An approach of integrating web services and Grid technology is proposed. Web service workflow technology is used to model the task of the Grid application and its requirement on resource services. The architecture of a Web service-based Grid supporting environment called WebSASE4G is introduced, which gives a new approach to Web service based Grid architecture.