A method for determining forwarding rule for data packet in Virtual Private LAN Service with Provider Backbone Bridge, PBB-VPLS, network capable of supporting multiple I-VPLS instances with different root sites and tree topologies by configuring one B-VPLS instance, the method being performed at a network side provider edge equipment, said method comprising: examining a value in a backbone service instance identifier, I-SID, field of the received data packet; and determining a virtual split horizon group, VSHG, corresponding to the data packet based on the I-SID value, then determining a forwarding rule for the data packet from said determined virtual split horizon group, VSHG, that is, which pseudo wire links of the PBB-VPLS network are forbidden or allowed to forward the data packet, the network side provider edge equipment forwarding the data packet, querying via said network side provide edge equipment a dynamic split horizon group table based on the I-SID value, thereby determining the virtual split horizon group, VSHG, corresponding to the data packet, wherein a dynamic split horizon group table records a relationship between the I-VPLS instance identified by the I-SID value and the virtual split horizon group, VSHG, the dynamic split horizon group table being generated and provided by a network management system and distributed to the said network side provider edge equipment, the dynamic split horizon group dynamically adapting to the different forwarding rules for the I-VPLS instances with different tree topologies, wherein each I-SID value uniquely identifies an I-VPLS instance, each virtual split horizon group, VSHG, value uniquely identifies a virtual split horizon group, and multiple I-VPLS instances are mapped to the same virtual split horizon group. examining a value in a backbone service instance identifier, I-SID, field of the received data packet; and determining a virtual split horizon group, VSHG, corresponding to the data packet based on the I-SID value, then determining a forwarding rule for the data packet from said determined virtual split horizon group, VSHG, that is, which pseudo wire links of the PBB-VPLS network are forbidden or allowed to forward the data packet, the network side provider edge equipment forwarding the data packet, querying via said network side provide edge equipment a dynamic split horizon group table based on the I-SID value, thereby determining the virtual split horizon group, VSHG, corresponding to the data packet, wherein a dynamic split horizon group table records a relationship between the I-VPLS instance identified by the I-SID value and the virtual split horizon group, VSHG, the dynamic split horizon group table being generated and provided by a network management system and distributed to the said network side provider edge equipment, the dynamic split horizon group dynamically adapting to the different forwarding rules for the I-VPLS instances with different tree topologies, wherein each I-SID value uniquely identifies an I-VPLS instance, each virtual split horizon group, VSHG, value uniquely identifies a virtual split horizon group, and multiple I-VPLS instances are mapped to the same virtual split horizon group.