The present invention discloses a method, an apparatus, and a system for forwarding a packet in a multi-topology network, relating to the field of communications technologies. The method includes: receiving, by an ingress node in the multi-topology network, a packet sent by a first network, and obtaining information of an ingress interface receiving the packet; where the first network is a network except the multi-topology network; obtaining a routing information base RIB or a forwarding information base FIB of a corresponding downlink topology according to the information of the ingress interface; and forwarding the packet to an egress node in the multi-topology network according to the RIB or the FIB of the corresponding downlink topology.