Abstract: A new dynamic access control scheme, in which an entity's behavior and privilege can be dynamically and flexibly linked, is proposed to improve scalability and to restrain cheating of resource sharing in traditional role-based access control scheme in grid environment. This new scheme can adjust a user's role by his behavior, setting up relationship between a user's privilege and his behavior. Combining this access control scheme with a trust model, the concepts of converting parameter and dynamic-role are introduced and applied to virtual organization (VO), in which converting parameter is designed to realize the reputation conversion among multi-domains. Simulations show that the system can easily realize access control, restrict malicious behavior of entities, and improve the scalability.