Aiming at the problem of low reliability of level signal as emergency command transmission, the optimization design is carried out from two aspects: hardware and software. In terms of hardware, through theoretical calculation of relevant parameters, optical relay is adopted to send instructions, and the circuit combination of instructions received by cable photoelectric coupler is adopted. In terms of software, emergency instructions are sent in the form of continuous pulses. After redundancy design, sliding window discrimination is carried out for the instructions received by FPGA at the receiving end to ensure the reliability of the instructions after receiving. After testing, the optimized instruction transmission interface has low power consumption, wide application and can realize long-term and reliable transmission of emergency instruction under 80m cable.