As the Web Service composition becomes complex, testing to ensure their quality and reliability become crucial. This paper extends traditional data flow analysis to Web Service composition testing. A test method for BPEL-based Web Service composition based on data flow analysis is presented. The test method is based on a test model called WSCTM that captures data flow test artifacts of Web Service composition. With the considerations of the intra-activity, intra-service, and inter-service, testing for Web Service composition based on data flow analysis can be accomplished in three levels, and various flow graphs are used to describe the interaction within and between services in structure model. The def-use chains of the Web Service composition can be obtained based on above analysis method. As a result, test paths can be selected to satisfy given criteria in order to achieve a desired Web Service composition test coverage.