Recently, Web service composition and optimization have received an increasing attention from both academia and industrial community. Most current methods have not paid enough attention to the user specific trust requirement for composite services. However, Trust is an important metric to judge whether a composite service can behave as user expected. In this work, firstly, a multifactor concept of trust of composite service is defined based on the trust of component services, interface compatibility and optimal binding schemes. Secondly, a trustworthy Web service composition and optimization framework called TWSCO is proposed to guarantee the trust of composite service and efficiency of Web service composition process. The interface-matching problem among component services and user preference are considered in TWSCO, which firstly uses component services filter to remove untrusted component services. Secondly, the concrete services, based on interface similarity, are organized as clusters. Thirdly, a composite template among component services is formed at the cluster level to guarantee the trust and efficiency of composite service. finally, the best binding scheme is discovered by an optimization method based on user specific trust metrics. In the end, experiments based on real Web services are presented to illustrate the proposed framework TWSCO can effectively guarantee the user preference trust of the composite service.