Semiconductor laser bars packaged with different thicknesses of solders and WCu submount are simulated using the multi-physical field simulation software of COMSOL Multiphysics. Results demonstrate that the maximum thermal stress of an In or AuSn solder occurs at the interface between the WCu submount and Cu heat sink. Thermal stresses of laser dies packaged using an In solder and an AuSn solder with the same thickness are 3.57 GPa and 3.83 GPa, respectively, and the corresponding wavelengths at the peak of spectrum are 800.5 nm and 798 nm, respectively. Reducing the solder's thickness is beneficial for reducing the thermal stress and temperature in the laser die. However, if the solder's thickness is too thin, it may cause weak welding of the laser core or uneven distribution of the solder, forming voids in the solder layer; hence, the selection of solder thickness should be considered as a whole. With increasing thickness of the WCu submount, the thermal stress of the laser die decreases; however, the temperature of the core rises. The optimal thickness of the WCu submount is 380 μm. This study provides a basis for optimizing the packaging of high-power semiconductor lasers and has guiding significance to practical production.