A method for transmitting multicast data, comprising: receiving, by a first Mobile Access Gateway, MAG, a handover message sent by a multicast source before its handover from the first MAG, to which the multicast source is currently accessed, to a second MAG, wherein the handover message carries identifier information of the second MAG; establishing, by the first MAG, a bidirectional tunnel between the first MAG and the second MAG according to the identifier information of the second MAG carried in the handover message; and multicasting by the first MAG, multicast data received from the multicast source via the established bidirectional tunnel, based on a determined post-handover multicast mode, wherein the post-handover multicast mode is a multicast mode adopted by the multicast source after the handover to the second MAG, characterized in that, the determining the post-handover multicast mode comprises: determining a multicast mode adopted by the multicast source after the multicast source accesses to the first MAG, and determining the post-handover multicast mode is a Rendezvous Point Tree, RTP, mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is a RPT mode; determining the post-handover multicast mode is an Shortest Path Tree, SPT, without multicast tree update mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is an SPT mode and that a moving speed of the multicast source is greater than a set threshold; determining the post-handover multicast mode is an SPT with multicast tree pre-update mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is an SPT mode and that a moving speed of the multicast source is not greater than the set threshold. receiving, by a first Mobile Access Gateway, MAG, a handover message sent by a multicast source before its handover from the first MAG, to which the multicast source is currently accessed, to a second MAG, wherein the handover message carries identifier information of the second MAG; establishing, by the first MAG, a bidirectional tunnel between the first MAG and the second MAG according to the identifier information of the second MAG carried in the handover message; and multicasting by the first MAG, multicast data received from the multicast source via the established bidirectional tunnel, based on a determined post-handover multicast mode, wherein the post-handover multicast mode is a multicast mode adopted by the multicast source after the handover to the second MAG, characterized in that, the determining the post-handover multicast mode comprises: determining a multicast mode adopted by the multicast source after the multicast source accesses to the first MAG, and determining the post-handover multicast mode is a Rendezvous Point Tree, RTP, mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is a RPT mode; determining the post-handover multicast mode is an Shortest Path Tree, SPT, without multicast tree update mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is an SPT mode and that a moving speed of the multicast source is greater than a set threshold; determining the post-handover multicast mode is an SPT with multicast tree pre-update mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is an SPT mode and that a moving speed of the multicast source is not greater than the set threshold. determining a multicast mode adopted by the multicast source after the multicast source accesses to the first MAG, and determining the post-handover multicast mode is a Rendezvous Point Tree, RTP, mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is a RPT mode; determining the post-handover multicast mode is an Shortest Path Tree, SPT, without multicast tree update mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is an SPT mode and that a moving speed of the multicast source is greater than a set threshold; determining the post-handover multicast mode is an SPT with multicast tree pre-update mode, if it is determined that the multicast mode adopted by the multicast source after the multicast source accesses to the first MAG is an SPT mode and that a moving speed of the multicast source is not greater than the set threshold.