Monitoring the basic component ir and the third component i3r of the resistive leakage current can reflect the MOA’s operation state. The harmonic voltages in the power system can influence the indication accuracy of ir and i3r. An improved capacitive leakage current compensation method is presented to extract resistive component from leakage current while harmonic voltages exist in power system. Simulation shows that this method can effectively eliminate the influence of harmonic voltages in power hystem. The measurement of resistive leakage current is more accurate.