A method for transmitting Multimedia Broadcast/Multicast Service (MBMS) data, comprising: sending, by a Broadcast/Multicast-Service Center (BM-SC), a Session Start Request with information of an MBMS service area to a Base Station Controller/Radio Network Controller (BSC/RNC) through a Gateway GPRS Support Node (GGSN) and a Serving GPRS Support Nodes (SGSN) of a core network; receiving the Session Start Request by the BSC/RNC, and building an Iu bearer plane by the core network and the BSC/RNC whose covering area overlaps the MBMS service area in the Session Start Request; allocating transmission resources for a data transmission of a MBMS service by the BSC/RNC whose covering area overlaps the MBMS service area in the Session Start Request, so as to provide the MBMS service to a user terminal. And the present invention also provides a system for implementing the method.