Embodiments of the present invention provide a method, an apparatus, and a system for data transmission. A network device receives a first multicast protocol packet sent by a network virtualization edge, NVE, for joining a multicast group, obtains first information, establishes an NVE interface of the multicast group according to the first information, and determines second information according to the first information, wherein the first information comprises a correspondence between each NVE connected to the network device and a multicast group to which each NVE belongs, and the second information comprises each multicast group in which the network device is involved; and sends the second information to a NVO3 manager, so that the NVO3 manager establishes a unicast tunnel interface of the multicast group between the network device and the at least one another network device according to the second information.