The complexity of the heat exchange equation brings difficulties to study laser-damage etc. A kind of stochastic method which treats the energy input and redistribution process as a chemical kinetics problem is used, and the thermal physical model is established. Based on stochastic method, the 2D distribution of temperature is studied by Gauss beam with 5 μm radius and 647 nm wavelength. The relationship of the temperature with irradiated time is obtained, and the effects on distribution of temperature are discussed about the variety of reflectance, absorption coefficient, thermal capacity and thermal conductance with temperature. The results indicate that stochastic method is reasonable to treat heat exchange, and the average of reflectance and thermal capacity can be used to improve simulating efficiency under the melting point of silicon.