The magnetic field energy harvester is suitable for the power source of sensors for power equipment state monitoring, with the advantages of easy installation and high power density. However, when the power line current is too high or the load is too large, the magnetic core used for energy harvesting may be driven into saturation region, resulting in the noise and heating, which affects the insulation performance of the magnetic field energy harvester and even threatens the safety of the monitored power equipment. To solve the above problems, this paper proposes a desaturation method for magnetic field energy harvester based on feedback winding compensation for the core protection. Meanwhile, the impact of feedback current phase and amplitude on the energy harvesting power and magnetic field intensity are analyzed. The proposed method can reduce the waveform distortion caused by deep saturation of the magnetic core. Finally, both simulation and experiments have verified the correctness and effectiveness of this method.