A thin surface layer always exists near the surface of laser heating melt pool due to the fluid flow driven by the surface tension gradient. In order to simulate accurately the fluid flow in the laser heating melt pool, the influence of the thin surface layer must be considered carefully. In this paper, the computational domain is divided into two regions, region I includes most part of the melt pool except for the thin surface layer on the top of the melt pool, i.e. region II . Comparison of simulated results using the two-region method with those using single-region method shows that one still can employ the single-region modeling approach to obtain correct isotherms and flow fields provided the mesh near the upper boundary is fine enough to resolve the surface layer.