A calculation method based on the relative diffraction efficiency of varied line-space blazed grating was presented in this paper，which is obtained through varied line-space grating diffraction intensity distribution formula.This method is simple，effective，although there is certain approximation，it is still instructive in engineering design.In addition，the influencing rule of varied line-space grating parameters on the diffraction efficiency is obtained，which provides a theoretical basis for the optimization of production process.