This paper presents a simulation model of a high-power semiconductor laser beam combining grating. This model analyzes the optical-thermal-stress change characteristics of the core device grating in the spectrum combining. The numerical analysis results show that when the power of the laser bar is 200 W and the natural convection coefficient is 10 W·(m²·K)^-1, the highest temperature on the diffraction grating can be increased to 346.52 K, and the highest stress point can be increased to 0.4825 Pa, The maximum deformation per millimeter of the grating surface is 52.28 nm, which will cause the center position of the feedback beam to shift by 0.25 to 0.3 mm, which will affect the laser power and beam combining efficiency. By reducing the thickness of the diffraction grating substrate and working under the same laser light source conditions, the changes in temperature, stress, surface shape and strain can be effectively suppressed, which is consistent with the experimental results. This method provides an effective multi-physics analysis method for the structural design of high-power semiconductor lasers and the testing and analysis of optical devices, and provides a comprehensive analysis numerical model for laser design and testing.