In terms of the theory of diffraction and nonlinear small-scale self-focusing,the analytical expression which described ripples of different spatial frequencies' passing through nonlinear media was induced. By analytical method,the nonlinear-gain characteristics of different spatial frequencies'wavefront distortions were obtained. The division method of the wavefront-distortion's spatial frequency was developed according to the requirements for the focal spot in drivers and the separation points between the higher,middle and lower frequencies which were assured according to the characteristics of domestic driver.