Abstract: Potential quality problems of standby reducer used in coal mine cannot be found because there is no loading test mean for high power reducer and only no-load test method. The paper introduced loading technologies used in mine machine field and analyzed advantages of AC frequency-conversion feedback loading technology. Then it described composition and working principle of an AC frequency-conversion feedback loading test system and gave main indexes of the system. The system can test working performances of the reducer with high power of coal mine under loading status, which has high testing efficiency and precision and perfect energy-saving effect.