Aiming at the reactance fault, bring forward a method of catching reactance faults based on FFT (fast fourier transform) algorithm, taking the FFT-model which belongs to Altium Designer Summer 09, analyzing the characterizations of the stability and synonym with serial-link circuits and parallel-link circuits of RLC, drawing the amplitude-frequency tide-lines of resistance and reactance by Excel, bringing out the tide analysis, and testing its feasibility and availability. As the result, this method turns to be able to catch reactance faults of circuits, and it can be used broadly.