Abstract: With the improvement of coal mine information and automation, the scale of coal mine power supply network is expanding, and reliable power supply and distribution system is the basic element to ensure the safety of coal mine production. The underground power supply monitoring system in this paper includes three key parts: underground monitoring sub-station, ground monitoring main station and communication system. The system collects the state parameters of underground equipment through single chip microcomputer technology, and each monitoring sub-station receives the data transmitted by terminal equipment through 485 bus, transmits it to the ground, and uses optical fiber technology to connect to the data server. Since the transmission direction of the system control signal is opposite to the access data transmission direction, the modbus-tcp protocol conversion can be used to realize the operation on the tcp/ip network, thus completing the test of the downhole power supply monitoring system technology. It can not only adapt to the complex underground environment, but also effectively monitor and control the underground power supply system in coal mine, and also ensure the safety of coal mine production.