The invention discloses a method, a device and a system for realizing data multicast. The method comprises the following steps: the transmission device receives a standby forwarding path establishment request, wherein the standby forwarding path establishment request comprises a device identifier and a destination address is an address of the multicast source device; wherein the equipment identifier is used for requesting to establish a standby forwarding path between multicast destination equipment identified by the equipment identifier and multicast source equipment; determining that the transmission device is located on a main forwarding path between a multicast destination device and the multicast source device according to the device identifier in the standby forwarding path establishment request; wherein the transmission device is not used as a device on a standby forwarding path between the multicast destination device and the multicast source device, and the standby forwardingpath establishment request is not forwarded. Therefore, when the transmission equipment fails, the transmission equipment only influences the main forwarding path of the multicast destination equipment and does not influence the standby forwarding path of the multicast destination equipment, so that the reliability of multicast data transmission is improved.