To identify the false QoS information and the complicity fraud between Web services, the paper adopts a QoS trust evaluation approach based on D-S evidence theory. This approach quantifies QoS information from both the public and private trust perspectives, which can determine the trustiness of Web services and identify the complicity fraud between the Web services. Preliminary simulation experiments show that, when the interactions between Web services increase, the approach can increase the success rate of trusted Web services, which is higher than the normal approach used before (which cannot identify false QoS information). The result supports the feasibility and effectiveness of the approach, prepares for the next large-scale empirical study.