Abstract: In view of problems of big pressure fluctuation and difficult adjustment in main pipe of air delivery when air compressor of a Coal Mine transports high-pressure air from interface to underground, a constant pressure air supply system of air compressor based on frequency-conversion speed-regulation and close-loop negative feedback control was designed. The system collects real-time pressure signal through pressure sensor in main pipe of air delivery, the pressure signal is compared with input pressure signal to get deviation signal. PLC analyzes and processes the deviation signal and outputs relative adjusting signal of frequency converter to make the frequency converter change power frequency of motor of air compressor, so as to adjust pressure of main pipe of air delivery. The actual application shows that the system realizes constant pressure transmission of high-pressure air in main pipe of air delivery with stable and reliable running.