With the continuous development of DC power transmission project, the DC current generated by it will invade the AC system, and the DC magnetic bias effect on the power system is becoming more and more serious. As the electromagnetic current transformer is the main metering device in the current power system, when the fault current flows through the current transformer, the hysteresis characteristics will lead to the distortion of the secondary side current of the transformer, which will lead to serious deviation in metering. Therefore, it is necessary to improve the accuracy of current transformer under fault current. Based on discrete wavelet transform and random forest model, the influence of fault current on current transformer is studied and analyzed, and the correction of secondary side distortion current is realized, and the proposed method is simulated. The results show that the method is effective for the correction of secondary side distortion current of ferromagnetic transformer.