In this paper, a numerical simulation of thermal process on the SMT laser microsoldering joint has been developed, in which, the influence on thermal process of the factors such as the thermal conductivity, variation of solder with temperature, light reflection coefficient of the lead wire surface, and heat exchange on the surface of SMT materials have all been considered. In order to carry this numerical calculation practice and prove it' s results, the reflexive characteristic of light wave to the SMT materials has been gauged temperature process of laser microjoint has been measured.