The essential principle of optical wavefront jitter for seeing- limited in large aperture telescope is presented.The mid and high frequency deviations from perfect wavefront are processed by power spectral density,which is used to evaluate the optic jitter.And it is applied to the plan wavefront measurement for laser,representing the jitter properties in frequency domain.This method contributes to the error analysis and budget of seeing limited optomechanical system and is useful as guidance for the evaluation of the wavefront quality.