Abstract: In order to realize the power quality detection of underground power supply system in coal mine, an on-line power quality detection system for coal mine is designed, which includes transformer, power quality online detection device host, mine communication base station, mine exchanger, etc. .The transformer is designed as flameproof type and adopts multi-tap independent winding voltage transformer. It can be applied to 3 kV, 6 kV and 10 kV voltage levels. The current transformer adopts multi-range current transformer and the maximum current on the primary side is 2000A.The detection host is designed to be flameproof and intrinsically safe. The hardware circuit based on DSP and MCU is designed, the C++ language is adopted as design the parameter measurement analysis software, design the evaluation method and evaluation flow based on the calculation of the electric energy quality time combination, and design the detection and management platform upper machine software based on Python language.The application indicated that the detection system was able to convert the collected data into the standard electrical energy quality data exchange format PQDIF, upload to the powering network detection and management platform, and realize data storage, calling, displaying, and generating a report.The system can easily set up monitoring points in all power supply facilities in the well, and realize on-line detection of the electrical energy quality of the power supply system in coal mines, achieve the full coverage of electrical energy quality detection of coal mine grids, comprehensively reflect the operation level of the grid in coal mines, and provide data support for the scientific assessment of the electrical energy quality and for the purpose of conducting governance and ensuring the safety and production of coal mines.