Abstract: The present invention is to provide a method of learning address in a VLAN system, which includes a plurality of network switching devices each connecting to at least one client VLAN and at least one server VLAN. Each of the network switching devices includes a forwarding database set therein, which includes at least a client VLAN forwarding table and at least one server VLAN forwarding table. When a network switching device receives a data packet from one of the client VLANs or the server VLANs, the network switching device firstly reads a source address contained in the data packet, and then learns the source address and stores the source address into a client VLAN or server VLAN forwarding table that matches the client VLAN or the server VLAN, and into a server VLAN forwarding table or all client VLAN forwarding tables that matches the server VLAN corresponding to the client VLAN or the client VLAN of the server VLAN.