Abstract: In order to study thermodynamic effect of 1070nm continwous wave fiber laser on three-junction GaAs solar cells, physical model was built by COMSOL software and numerical simulation was carried out. Thermal stress fields under different laser power densities were obtained. In order to verify the correctness of thermal stress calculation method, surface deformation of batteries under laser irradiation with power of 16.7W, irradiation radius of 1mm and irradiation time of 10s was measured by grating projection method. The simulation results show that, when irradiation radius is 1.5cm and power density is 16.7W/cm², laser irradiation time is 20s, central temperature of bottom battery is just above service temperature of the battery. Equivalent stress in the center of bottom battery is 96.6MPa. It just exceeds the yield limit of bottom battery material. According to this result, it can be inferred that the failure of battery is related to the structural damage caused by thermal stress. The experimental results are in good agreement with the simulation results. The numerical simulation results and experimental results provide theoretical basis for the study of thermal effects of laser irradiated solar cells.