According to the Fourier heat conduction theory and thermal stress field theory, the COMSOL simulation software and Matlab software are used to construct the combined damage model of three-junction GaAs solar cell under combined laser irradiation, and the temperature and stress field distribution of solar cell under single millisecond laser irradiation and combined pulse laser irradiation are calculated. The results show that, compared with single-millisecond laser, the combined laser irradiation can produce a wider melting damage area and obvious stress damage, and the damage area and depth will increase with the increase of energy density and action time delay of nanosecond pulse laser. When the energy density increases to 0.5 J/cm ², the radius and the depth of the melting damage spot are risen to 2 mm and 1.5 μm, respectively. When the time delay increases to 0.5 ms, the radius and the depth are increased to 1.4 mm and 1 μm, respectively.