An IP multicast system includes: an IGMP proxy unit set in an access network which provides information of a multicast group to which a terminal belongs. The IGMP proxy unit receives data sent from a multicast data source, and sends the data to a base station which then sends the data to the terminal. The IGMP proxy unit simplifies IP multicasting in the mobile network and makes the transfer of multicast data transparent with respect to the core network of the mobile network. This system can support mobile communication networks as WCDMA, CDMA2000, GSM and TD-SCDMA.