In order to quickly check the leakage point, the leakage detection system is widely used in the low voltage radio station area ("station area"). Due to the zeroorder harmonic caused by the nonlinear load in the station area, the accuracy of leakage current detection in the leakage detection system is seriously reduced, and the existing frequency domain filtering method is difficult to measure the transient leakage current accurately. Therefore, a separation method of leakage current base wave and harmonic component is proposed, that is, a singlephase dq transformation filtering method. Comparing with the frequency domain filtering method, It can suppress the zeroorder harmonics in the station line well without causing the attenuation of the temporary leakage current base wave value. The leakage current is detected by the leakage system and the problem of zeroorder harmonic interference is then solved. The feasibility of the method is verified by MATLAB software simulation finally.