This application provides a multicast service implementation method and apparatus. The method includes: receiving, by a first network device, a first unicast join message sent by a second network device, where the first unicast join message is used to request to join a multicast group, a source address of the first unicast join message is an address of the second network device, and a destination address of the first unicast join message is a multicast source address or a rendezvous point (RP) address; and establishing, by the first network device, a tunnel from the first network device to the second network device based on the first unicast join message. The multicast service implementation method and apparatus in embodiments of this application help improve availability of a multicast service.