A data transmission method for a data transmission system including a host and a peripheral device is disclosed, including: setting at least one identification number to at least one packet stored in the host; transmitting the at least one packet from the host to the peripheral device; allocating the at least one packet to plural temporary blocks of a memory of the peripheral device corresponding to the at least one identification number according to the at least one identification number of the at least one packet. Each of the temporary blocks includes a threshold value, and the threshold value of each of at least two of the temporary blocks are different; and transmitting part of the at least one packet stored in one of the temporary blocks when the one of the temporary blocks reaches the threshold value of the one of the temporary blocks.