The utility model discloses a demagnetization circuit for an excitation system. The system comprises a pair of demagnetization components and an annular core. Each of the demagnetization components comprises a demagnetization module and a silicon-controlled element arranged on the demagnetization module. The demagnetization circuit also comprises a pair of resistance-capacitance adsorbing circuits, a pair of demagnetization impedance circuits and a Hall effect sensor. Two ends of each of the resistance-capacitance adsorbing circuit are respectively connected to two ends of the silicon-controlled element of each of the demagnetization components. One end of each of the demagnetization impedance circuits is connected to one demagnetization component, and the other end of each of the demagnetization impedance circuits is connected to an outer rotor. The Hall effect sensor is arranged in the annular iron core gas gap of the demagnetization circuit. According to the demagnetization circuit, the monitoring of the current in the demagnetization impedance circuits by a Hall sensor can be realized, the interference of the Hall sensor by the resistance-capacitance adsorbing circuits is avoided, thus the Hall sensor can effectively and accurately judge whether the current in the demagnetization impedance circuits is higher than the setting value of a generator system, and the loss caused by wrong judgment is reduced.