In this paper, we propose a scalable service scheme for secure group communication in grid. In the service scheme, a series of methods and strategies are presented, such as the initialization methods for group member, administrative domain and virtual organization, the key distribution strategy and the rekeying strategy. In order to improve the scalability of this service scheme, the services for a group are logically divided into two hierarchical levels, which is in accordance with the characteristics of group communication in grid. In addition, in order to show the efficiency and the scalability of the service scheme, simulation experiments are done. The results show that the service scheme is efficient and scalable. Thus, the service scheme can satisfy the requirement of people in large-scale, dynamic grid environment.