In service-oriented computing applications, service consumers and providers need toevaluate the trust levels of potential partners before engaging in interactions. The accuracyof trust evaluation greatly affects the success rate of the interaction. Trust evaluationis a challenging problem in open and dynamic environment as there is no centralmediator to manage standardized evaluation criteria or reputation records. In this paper,a novel trust model, called the priority-based trust model, is presented. The model derivesthe trustworthiness of a service provider from designated referees and its historicalperformance. In addition, consumers can specify their preferred priorities which will affectthe result of trust evaluations. The experimental results show that the proposed model hasbetter performance than other trust models, especially in open and dynamic environments.