The detection of leakage faults in the high-voltage system of electric vehicle is actually the testing of the high-voltage insulation performance of electric vehicle. The online monitoring system for electric vehicle faults based on electromagnetic effects uses high-precision Linear Hall Effect Sensor to equivalently measure the leakage current of the high-voltage wiring harness of electric vehicle. At the same time，the method of setting threshold values is used as the judgment condition for the level of leakage faults， achieving online electric vehicle of leakage in the high-voltage system of electric vehicle and ultimately providing guarantees for human and vehicle safety.