It is a challenge to integrate and share resources securely across multiple autonomous administrative domains environment. This paper introduces the Community-Based Model of Vega Enterprise Information Grid and its operation mechanism. The individuals and/or institutes forming different communities can not only implement diverse policies and autonomous management of resource sharing without any impact on the other communities, but also achieve a globally shared goal. Based on the model, the access control technique, including framework and uniform formalizing, is presented in detail. The static or dynamic role binding is used for entitling user's request for accessing resources within or across communities, which ensures a globally unified view for user. A prototype describes how these techniques are useful in building an enterprise information grid. The evaluation and future continuing works are presented in the conclusion.