As an important part of the mine production system, the coal mine drainage system plays an important role in mine production. In order to meet the needs of coal mine drainage and achieve the reliability, safety, real-time, and automatic operation of the drainage system, the underground hardware design of main drainage automatic control system was studied, with the introduction of the selection of the PLC, the address allocation of the input and output of the PLC module, the hardware connection of the PLC control system, and the power supply design inside the programmable control box. The module has a total of 2 communication ports, 18 analog input points, 37 digital output points, and 47 digital input points. The study provided a basis for the software design of the system and ensured the safe operation of the underground main drainage automatic control system.