A method is proposed for designing the grating splitter with plane-surface-relief. Ray tracing theory is used to obtain phase and universal polynomial function of grating,and the coefficient of the polynomial function is optimized by genetic algorithm. Several grating splitters with ratio 1:2×2,1:3×3,1:4×4 and diffraction efficiency 81.83%,81.11% and 74.01%respectively are designed based on the method. The simulation made by Matlab software shows that the intensity uniformities of the three gratings designed through the method achieve 0.023 94,0.183 8 and 0.191 2 respectively,which indicates that the method has universal compatibility for designing the diffraction optics components.