A method for relay multicast transmission, comprising: sending, by a first terminal, a relay selection request to a relay selection server; determining, by the relay selection server, according to the relay selection request, multiple second terminals which will communicate with the first terminal, and a multicast relay node corresponding to at least two second terminals, and sending a relay multicast notification to the first terminal and the multicast relay node separately; sending, by the first terminal, a piece of data to the multicast relay node, according to the received relay multicast notification; and according to the received relay multicast notification, copying, by the multicast relay node, the data from the first terminal, and multicasting the data to the at least two second terminals corresponding to the multicast relay node, characterized in that, in case of a multi-part conference, the relay selection request includes a multi-part conference request for that the first terminal will proceed a multi-part conference with multiple second terminals, the first terminal and any of the multiple second terminals can become a source terminal or a target terminal of the multicasting data, and the relay selection request includes addresses of the multiple second terminals that will communicate with the first terminal, the relay selection server further sends a relay multicast notification to at least two second terminals corresponding to the multicast relay node separately according to the relay selection request; and according to the received relay multicast notification, either of the at least two second terminals sends a piece of data to the multicast relay node, the multicast relay node copies the data from the either of the second terminals and multicasts the data to the other of the at least two second terminals and the first terminal. sending, by a first terminal, a relay selection request to a relay selection server; determining, by the relay selection server, according to the relay selection request, multiple second terminals which will communicate with the first terminal, and a multicast relay node corresponding to at least two second terminals, and sending a relay multicast notification to the first terminal and the multicast relay node separately; sending, by the first terminal, a piece of data to the multicast relay node, according to the received relay multicast notification; and according to the received relay multicast notification, copying, by the multicast relay node, the data from the first terminal, and multicasting the data to the at least two second terminals corresponding to the multicast relay node, characterized in that, in case of a multi-part conference, the relay selection request includes a multi-part conference request for that the first terminal will proceed a multi-part conference with multiple second terminals, the first terminal and any of the multiple second terminals can become a source terminal or a target terminal of the multicasting data, and the relay selection request includes addresses of the multiple second terminals that will communicate with the first terminal, the relay selection server further sends a relay multicast notification to at least two second terminals corresponding to the multicast relay node separately according to the relay selection request; and according to the received relay multicast notification, either of the at least two second terminals sends a piece of data to the multicast relay node, the multicast relay node copies the data from the either of the second terminals and multicasts the data to the other of the at least two second terminals and the first terminal.