Abstract: Semiconductor laser beam splitting technology can achieve near-diffraction limit of high-power laser output, and has become the current research focus. Performance of diffraction grating directly determines laser output effect of spectral beam. A sub wavelength transmission grating for 940nm wavelength and fused silica material is simulated and designed. Based on strictly coupled wave theory, grating structure is designed, and parameters such as grating duty cycle, ridge height and period are optimized by Rsoft software. Influence of each parameter on diffraction efficiency of grating is also analyzed simultaneously. Designed diffraction grating achieves wavelength division multiplexing function of -1 diffraction order, diffractive efficiency reaches 91.2% for TE mode, and diffraction efficiency is reduced to 1.2% or less by compressing other diffraction orders. Diffraction efficiency of 90% or more is maintained within range of grating incidence angle of 59°±3°, meanwhile high power laser output has high error tolerance, and is easy to adjust to meet requirements of spectral beam combination technology.