The utility model relates to an on-line monitoring system of a magnetically controlled reactor. The on-line monitoring system comprises an HFCT monitoring system, a partial discharge monitoring system, a vibration monitoring system, a temperature monitoring system an oil chromatography monitoring system. The on-line monitoring system determines partial discharge in a reactor by use of an ultrasonic wave detection method, detects temperature in the magnetically controlled reactor by use of a built-in thermal resistor, and determines types of faults of the magnetically controlled reactor in a crossed manner by use of the oil chromatography monitoring system, the HFCT on-line monitoring system, the vibration monitoring system and a current detection system.