A serial transmission controller, a serial transmission decoder and a serial transmission method thereof are disclosed. First, a current address and an access address are compared to select one of a plurality of transmission address modes as an access address mode and then to produce corresponding address information. The transmission address modes use different bits to transmit the address information respectively. According to the access address mode, an access command is selected from a serial command set. Finally, the access command and the address information are transmitted to a serial interface serially. After the access command is encoded to different length of bits, the encoded access command is transmitted to the serial interface so as to reduce the transmission bits and improve the transmission efficiency.