The invention discloses a method for detecting the blade structural damage of a wind power generator based on spectral analysis, comprising the following steps: 1) calculating the spectral characteristic of each blade vibration signal of the wind power generator; 2) calculating the spectral area of the spectral characteristics of blade vibration signals with frequencies greater than NHz; 3) calculating a spectral area difference of the blade vibration signals in a blade flapwise direction and a spectral area difference of the blade vibration signals in a blade edgewise direction; 4) when the spectral area difference of the blade vibration signals in the blade flapwise direction is greater than a preset value of the spectral area difference in the flapwise direction, determining that the initial damage occurs on the blade flapwise surface; and when the spectral area difference of the blade vibration signals in the blade edgewise direction is greater than a preset value of the spectral area difference in the edgewise direction, determining that the initial damage occurs on the blade edgewise surface, so as to complete the detection of the blade structural damage of the wind power generator based on spectral analysis. The method can realize real-time online detection of the blade structural damage of the wind power generator.