Abstract: A method is proposed to construct direct trust model based on QoS (Quality of Service) constraints provided by the services,and a partial relation is introduced to shield the worthless history record in the building process.Meanwhile,the recommendation trust model is constructed by referring to the behavior rules of human society,and the malice recommendation information is shielded by using the marking mechanism of contest in human society.In order to avoid load imbalancing,a service selection based on the method of roulette wheel is adopted.Experiment proves that this model is effective.