The invention discloses a method for realizing cross-VPN multicast, which comprises that: PE on a multicast source and PE on a customer are all provided with a virtual switch instance (VSI) of a VPN where the multicast source is positioned, and pseudo wire (PW) connection is established in the VSI; a multicast router sends an internet group management protocol (IGMP) general query message in the VPN where the multicast source is positioned, and uplink router port information of the VPN where the multicast source is positioned is respectively formed in the PE on the multicast source and the PEon the customer; the PE on the customer and the PE on the multicast source maintain a local multicast member relation table respectively according to sensed multicast information carried in an IGMP protocol message initiated by a user in a VPN where a non-multicast source is positioned; and when receiving multicast data streams, the PE on the multicast source and the PE on the customer retrieve the locally stored multicast member relation table respectively according to the VPN ID where the multicast source is positioned and a multicast MAC address, and then forward the multicast data streamsthrough downlink outgoing interfaces of retrieved entries.