The research work of RBAC is greatly emphasized in recent years. However, the main work focuses on some characters which have nothing to do with the time character. A RBAC model with time character called TRBAC is described and the former constraint is extended so that it can describe the time character. Some algorithms are developed to solve the state change problem of the time-constraint and the sessions. The consistent state of the model is analyzed and the problem for maintaining the consistent state is discussed.