The invention discloses a coding circuit design method applied to optical fiber transmission. The method comprises coding processes and decoding processes: a coding process for collecting collection data in an FPGA and a decoding process for a control command, and a decoding process for controlling the collection data arranged in the FPGA and a coding process for the control command. According tothe method provided by the invention, the mode of combination of a synchronous head and a complete balanced code is used; the synchronous head and a transmission protocol are self-defined; a coder, decoder, a parallel-serial conversion circuit and a serial-parallel conversion circuit are designed, and thus bidirectional transmission of the high-voltage collection data and the low-voltage control command can be achieved through only connecting an external optical fiber transceiver; a hardware circuit is simple to design, and can completely replace a special chip and meet high voltage isolationtransmission requirements, and real-time uploading of the high-voltage end collection data and downloading of the low-voltage end control command are achieved.