The invention belongs to the technical field of power equipment and particularly relates to a lightning arrester resistive current online monitoring method based on a Blackman bimodal interpolation harmonic analysis method. For the zinc oxide arrester (MOA) resistive current online monitoring, the inhibition of frequency spectrum leakage and a fence effect under signal asynchronous sampling basedon the Blackman bimodal interpolation harmonic analysis method is adopted. According to the system, a current signal and a voltage signal sampled from a lightning arrester are converted into digital signals, then the signals are sent to a microprocessor for fast discrete Fourier transform, the signals are analyzed in a frequency domain, an appropriate window function is selected to suppress the long-range leakage of the signals, and the interpolation correction is carried out on the amplitude, the phase and the frequency of the signals in the form of the window function.