In order to research nonlinear absorption effect of pulse laser irradiation for GaAs,a physical model of Gaussian distribution pulse laser irradiation for semiconductor material was established by software COMSOL Multiphysics. The thermal effects of semiconductor material GaAs was analyzed under irradiation of nanosecond pulse laser with wavelength of 1064nm. The temperature distribution along radial direction and longitudinal direction of semiconductor material GaAs was calculated under irradiation of nanosecond pulse laser with different power density by means of solving the thermal conduction equations. The contribution of one-photon absorption, two-photon absorption and free carrier absorption to temperature of the irradiated material was discussed. The calculation results show that when the pulse laser power density is above 1010W/cm2, Free Carrier Absorption played a leading role and is more than that of One-Photon Absorption of material. When the pulse laser power destiny is below 108 W/cm2, the temperature contribution of two kinds of nonlinear absorption of materials could be ignored. The result is basically consistent with relevant experiments, which shows that physical model constructed is scientific.