This paper integrates QoS to trust model. An approach for trust computing using FCMs and D-S evidence theory are presented. Compared with existing models, our model has some main features. First, it eliminates malicious recommendation by considering QoS. Second, As fuzzy inference can deal with variable dependencies in the system by decoupling dependable variables, the FCMs approach provides an efficient way to trust deducing, and also the difficulty and complexity of trust computing. Finally, the approach of D-S evidence overcomes the problem of over-precision.