This paper presents an efficient multicast method based on a locality in mobile IPv6 networks. We exploit the repetitive movemnent pattern of mobile node to reduce number of experience of graft and join procedure. We defined the locality scope by a movement pattern. While the network is included in the locality scope, the network should maintain a multicast tree even when the mobile node moves to the other network. In this way, the mobile host can receive a multicast service without a delay when it moves to the network in the locaility scope later. We compare our scheme with existing schemes under the total signaling cost and the service delay time by using a discrete analytical model for cost analysis. Analytical results demonstrated that the total signaling cost and service delay time was significantly reduced through our proposed scheme.