The present invention discloses a data transmission system. The data transmission system includes a processing unit, a first serial peripheral interface circuit, and a first display interface circuit. The processing unit is arranged to determine a length of a file, divide the file into at least one sub-file according to a system resolution, and produce a file transfer command. The first serial peripheral interface circuit is arranged to transmit the file transfer command to a second serial peripheral interface circuit. The first display interface circuit is arranged to transmit the at least one sub-file to a second display interface circuit, sequentially.