Abstract: To realize high real-time and high-precision detection of rectangular wave signal with equal duty ratio,a method of frequency-equal-square-wave square-wave method was proposed,which was based on fast Fourier discrete spectrum analysis.Through the combination of theoretical analysis,MATLAB simulation and field experiment,this article compared the Fourier Frequency Measurement of Hanning Window,the direct Fourier frequency method,the hardware filtering method with the method of frequency-equal-square-wave square-wave method etc.about the test accuracy and error under different frequency.The results showed that the high - order harmonic - weighted frequency measurement method has obvious advantages over the other two kinds of Fourier frequency measurement methods in the measurement accuracy and variance under the condition of limited sampling samples and high real - time requirements,especially at low frequency side.In the absence of spike error,the measurement accuracy of the hardware frequency measurement accuracy is similar to high - order harmonic - weighted frequency measurement method. But in the strong electromagnetic interference,the high harmonic frequency measurement method has obvious advantages.