Single junction GaAs solar cells were irradiated by 808 nm and 10.6 μm continuous wave lasers respectively. The results show that, as long as under the same laser coupling intensity, the damage modes of solar cells under two different irradiation conditions are similar. As the laser coupling intensity increases, the maximum output-power of solar cells shows a ′stair-step′ decline. Damage processes was further investigated through analysis of temperature rising rate, peak temperature, duration of high temperature and variance, as well as energy disperse spectroscopy and scanning electron microscope measurements. It is found that the high temperature during irradiation process leads to the dissociation of GaAs and the oxidation of the electrodes, which further results in performance degradation of single junction solar cells.