The invention discloses an electricity stealing detection method based on Fourier transform. The method comprises the following steps: injecting a time-varying harmonic signal into a power grid at anentrance meter of a user to be analyzed; acquiring a voltage signal and a current signal at the first sampling frequency at user ammeters and a gateway meter; weighting voltage and current sampling sequences with a high-resolution window; performing short-time Fourier transform on the weighted voltage and current sampling sequences, and calculating the magnitude and a corresponding phase of each sub-harmonic wave; calculating the instantaneous power of each user ammeter and the instantaneous power of the gateway meter; performing initial electricity stealing detection; sampling the voltage signal at the gateway master at the second sampling frequency, and calculating the dynamic frequency of each inter-harmonic wave; and performing secondary confirmation on the initial electricity stealingdetection result to obtain a final electricity stealing detection result. The method has the advantages of simple calculation process, and accurate judgment of electricity stealing behaviors and location of electricity stealing users. A fast and effective way is provided for anti-electricity stealing detection of a power system.