Based on optical interference theory and Fourier modal theory, a new multi-layer dielectric gratings is designed for use in femtosecond laser system at wavelength 0.8μm. A multi-layer dielectric with stack of H3L(HL)^9H0.5L2.4H is used as a substrate to be etched with corrugated structure. Numerical computation indicates that the diffraction efficiency of -1 order can be more than 95% when the parameters of multi-layer dielectric grating are the following: laser is incident on the grating at 36.7° in TE mode, the duty cycle is 0.35 and the line density is 1480/mm, the groove depth is 0.2μm and the top residual HfO2 is 0.15μm.