A printing system includes a portable communication device, a printing device and plural transmission channels. The printing device is used for receiving a to-be-printed data from the portable communication device, thereby performing a printing task. The plural transmission channels are selectively in communication with the portable communication device and the printing device for transferring the to-be-printed data to the printing device. The portable communication device includes a controlling unit for judging and setting priority values of the transmission channels and selecting one of the transmission channels as a priority transmission channel according to the priority values of the transmission channels, so that the to-be-printed data is transmitted from the portable communication device to the printing device through the priority transmission channel.