With the development of information systems in Internet, user authentication and authorization management gradually become one of the biggest concerns. To solve the problem, this paper presents a role-based PMI authentication model. In the framework of the model we use role specification certificates(RSC) and role assignment certificates (RAC) to achieve secure access control to network resources. The model has been applied to an enterprise network for the privilege authentication processing. The practice shows that the model can be used to simplify authorization administration and provide expansibility and flexibility.