Abstract: Ｔhe power spectral density(PSD) has been employed as the specifying parameter of the optical components with large aperture in the testing process. According to the different wavefront modulation with different depth or frequency, the PSD curves present different variation rule. The change of the modulation frequency will change the corresponding frequency value of the protuberant part on the PSD curve, and at the same time the peak value of the protuberant part is changed. Ｔhe modulation depth is focused on the intensity change of the protuberant part of the PSD curves．Ｉt cannot influence the frequency value of the protuberant part.