Abstract: The traditional RBAC model has less flexibility to assign permissions of users．This paper proposed an improved RBAC authorization model based on time partition．The whole system process is divided into several time partitions．The permissions associated with each role are distributed in each independent partition．The set of stages which have the permissions of each time partition constructs the improved RBAC model by combining the basic RBAC model．When the stages are determined,the permissions of roles and users can be configured by the administrator．The proposed RBAC model is applied in public selecting system stably and obtains good performance.

Key words: RBAC,Access control,Time partition,Stage