SaaS as a service is a new software mode which deploy the application on the local server and provides application software service for customers through the Internet. Based on the study of the traditional RABC mode and combined with the characteristics of multi-tenant, configurability and personality, the author of this article has designed a hierarchical mode of SaaS system for access control model. It achieves the function multi-tenancy and personalized service of system and then provide the design proposal and the implementation principle.