Software defect is an important indicator for measuring the adequacy of software testing. In order to improve the reliability and robustness of Web service composition based BPEL, this paper proposes a defect detecting method which combines the dead path into a path sensitive analysis. Dead path is a special semantic of BPEL, which has no execution information, but can connect two executed path segments. Using the abstract value of variable and its interval arithmetic, this method can identify an unreachable path and dead path, and also merge the conditions of property state at join points. A case study about uninitialized variable detecting which is related to dead path and executing path is given throughout the analysis, and verification is implemented to illustrate the effectiveness of this approach.