Abstract: Motor current characteristic analysis has become a widely used technology for fault diagnosis of induction motors. However, its industrial applications face practical problems. One of the most challenging scenarios is that the spectral components of the fault characteristic harmonics can be covered by the spectral leakage of the power supply frequency component even under severe faults. Different solutions to this problem have been proposed, such as the use of sliding windows, advanced spectrum estimation methods, etc. However, these methods merely change the spectrum content of the current signal or increase the amount of computation. Base on it, a new method was proposed to refine the spectrum analysis of the current by simply zeroing the time-domain current sampling signal, which can accurately estimate the actual power supply frequency, and then extract the original spectrum with almost no leakage. The effectiveness of the proposed method was verified by Matlab signal test.