The influence of cutting parameters on the frequency characteristics of optical crystal surface has been studied. The experiment of single point diamond turning was adopted to process KDP crystal. The frequency distribution of surface profile was obtained by power spectral density. The continuous wavelet method was used to evaluate the influence of cutting depth, feed rate and spindle speed on machined surface. The results show that the frequency characteristics reflect the effects of cutting parameters on surface topography. The wavelength and amplitude of mid frequency embody the change of cutting depth and spindle speed, and the amplitude increases with the increase of cutting depth and speed. Low frequency reflects the change of feed rate, and the amplitude becomes small as feed rate decreases. High frequency is the manifestation of vibration and material anisotropy in processing. Therefore the analysis of frequency characteristics on surface topography provides a reference for selecting the optimal process parameters.