The invention relates to a power grid fundamental frequency detection method based on spectral extreme points. Time-domain sampling of the voltage or current of a power grid is carried out at a predetermined sampling frequency to get a discrete time sequence of voltage or current. Sliding discrete Fourier transform or fast Fourier transform is carried out on the discrete time sequence to get a spectrogram of voltage or current. According to the method of the invention, the voltage or current signal of the power grid is digitally measured at a fixed sampling frequency, discrete Fourier transform or fast Fourier transform is carried out on a collected discrete time sequence of voltage or current to get a spectrogram of voltage or current in the frequency range from 49.5Hz to 50.5Hz, and the fundamental frequency of the power grid is detected according to the spectral extreme points.