The invention discloses an FFT data correction method in the detection of the stay cable force of a cable-stayed bridge with a frequency method; an acceleration sensor is arranged on a stay cable and connected with a control box; a fundamental frequency generation module is arranged inside the control box; the fundamental frequency generation module comprises an FFT module, a waveform correction module and a secondary FFT module; the acceleration sensor captures a time-domain vibration signal of the stay cable and inputs the signal into the control box; the time-domain signal is then processed through FFT spectral analysis by the FFT module, so that the spectrum curve of the signal can be obtained; the data of the frequency within 7.5-25Hz on the spectrum curve is kept, while the remaining data is made zero; after the data of the frequency within 7.5-25Hz obtained in the third step is processed through secondary FFT transformation analysis by the secondary FFT module, the fundamental frequency of the stay cable of the cable-stayed bridge can be detected. Through the FFT spectrum analysis data correction and the secondary FFT transformation, the invention can accurately detect the fundamental frequency of the stay cable of the cable-stayed bridge and eliminates the abnormal phenomena due to the cable force detection through a frequency method.