Femtosecond laser with ultrashort pulse (≤35fs) is used to investigate the damage threshold and light-to-electric conversion efficiency of gallium arsenide solar cells. Different from nanosecond or picosecond lasers, the damage threshold of the solar cell illuminated by femtosecond laser is slightly higher than that under the illumination of continuous-waves laser with the same wavelength. Because the thermal non-equilibrium effect becomes obvious, heat conduction phenomenon no longer obeys the law of Fourier, when the heating pulse time of femtosecond laser is equal to or shorter than the electron-phonon coupling time. The photovoltaic properties of gallium arsenide solar cells under femtosecond pulse laser illumination are measured. The device shows better short circuit current and the light-to-electric conversion efficiency under femtosecond pulse laser than that under continuous-waves laser of the same wavelength.