A data transmission method for classifying network connections and transmitting multimedia data is described. After distinguishing multimedia connections from non-multimedia connects, multimedia packets are classified and consolidated into packet groups and then the packet groups are transmitted. The method for transmitting multimedia data comprises the following steps. First, determine whether a connection is used for transmitting multimedia data or not. If it does, the packets are consolidated into a packet group. Finally, forward the packet group according to a predetermined order after the packet group is assembled.