A data packet transmission method and a LAN switch device, the method includs: the LAN switch device learns the member port which corresponds to the VLAN according to the data packet received by the LAN switch, and stores the learned corresponding relationship between each VLAN and its member port, transfers the data packet according to the stored corresponding relationship between each VLAN and its member port. The memory space of the MAC address table of the LAN switch device of the present invention only need to meet the MAC address of the local user, it reduces the MAC address table storing space of the LAN switch device demanded by the converge network; the corresponding relationship between the VLAN and its member port stored in the LAN switch device of the present invention only relates to the number of the VLAN, and has no relation to the number of the user accessing the network, it can access more users to the converge network, which is advantageous to expand the network; therefore, it reduces the organization price of the converge network.