A method for implementing multicast service, characterized in that the method implements multicast service in a Location Identification Separation Network, LISN, identifies a multicast service packet between an Access Service Router, ASR, and terminals by using a Group Access Identity, GAID, and uses a Group Router Identity, GRID, to identify the multicast service packet in a core network, the method comprising: a multicast source sending a multicast service packet, a destination address of the multicast service packet being configured to be the GAID assigned to the multicast source, and a source address of the multicast service packet being configured to be an Access Identity, AID, of the multicast source; after receiving the multicast service packet, an ASR to which the multicast source belongs searching for a corresponding GRID in an established GAID-GRID mapping table according to the GAID, and searching for a corresponding Router Identity, RID, in an established AID-RID mapping table according to the AID; the ASR to which the multicast source belongs replacing the GAID of the multicast service packet with the GRID, and replacing the AID of the multicast service packet with the RID; or the ASR to which the multicast source belongs adding the GRID and the RID into the multicast service packet; the ASR to which the multicast source belongs sending the multicast service packet to a General Switch Router, GSR, in the core network; the GSR searching for a corresponding multicast tree according to the GRID of the multicast service packet, and sending the multicast service packet to the ASR in a service area according to the multicast tree; an ASR in the service area searching for a corresponding GAID in a locally stored GAID-GRID mapping table according to the GRID, searching for a corresponding AID in a locally stored AID-RID mapping table according to the RID, replacing the GRID of the multicast service packet with the GAID, and replacing the RID of the multicast service packet with the AID; or the ASR in the service area removing the GAID and the RID in the multicast service packet, searching for a corresponding GAID in a locally stored GAID-GRID mapping table according to the GRID, and replacing the GRID of the multicast service packet with the corresponding GAID; and the ASR in the service area sending the multicast service packet to a terminal under the ASR in the service area; before sending the multicast service packet, the multicast source applying for the GAID and the GRID and requesting an identification location register for performing authentication after obtaining the GRID; if the authentication succeeds, the ILR sending the GAID and the GRID of the multicast source to the ASR in the service area; and the ASR in the service area establishing the GAID-GRID mapping table after receiving the GAID and the GRID; the ASR in the service area further broadcasting the GAID to terminals under the ASR in the service area after receiving the GAID and the GRID; the terminal under the ASR in the service area determining whether to receive a multicast service identified by the GAID according to the received GAID, if yes, requesting the ASR to which the terminal belongs to open the multicast service; the ASR in the service area requesting an upper layer GSR for joining in a service group of the multicast service identified by the GAID according to the request of the terminal; and the GSR adding a route reaching to the ASR which sends out the request into the multicast tree according to the request of the ASR. a multicast source sending a multicast service packet, a destination address of the multicast service packet being configured to be the GAID assigned to the multicast source, and a source address of the multicast service packet being configured to be an Access Identity, AID, of the multicast source;