The existing QoS(quality of service)-based services selection approaches always assume that the QoS data coming from service providers and users are effective and trustworthy, which is actually impossible in reality. A service selection approach based on the authenticity of QoS data and workflow model was proposed to solve the problem. For the QoS data coming from service providers, the statistics of past runtime data to revise the providers' QoS data were used. For the subjective evaluation coming from users, the confidence values of users were calculated based on the workflow-organization-model, and then the evaluation was computed by using the confidence. At last, the optimal web services could be selected by combing the two values as the judgment standard. The experimental results show that this approach can effectively weaken the influence of untrustworthy QoS data on Web service selection and strengthen the accuracy of service selection.