Abstract: A one-domain mixture continuum model is used to simulate numerically solid/liquid phase transformation with a mushy region during laser welding process of 1Cr18Ni9Ti stainless steel.Emphasis is given to the competitive influence of laser-induced alloying element vaporization and surface tension on the heating surface maximum temperature,its distribution and the convective flow in the molten pool.The pool development,transient heat and fluid flow fields have been computed under five computational cases corresponding to five different pool surface heat flux balances.The results show that the Langmuir vaporization heat loss of Fe,Mu,Cr,Ni elements can significantly reduce the heating surface maximum temperature when |∂σ-∂T|is small or the driven force acting on the pool liquid is only buoyancy,However,when the vaporization heat loss and surface tension are co-existing,the temperature distribution and its maximum temperature on the pool surface are dramatically affected by the magnitude order of surface temsion gradient and the nature of the relationship between surface tension temperature coeffcient and temperature.When |∂σ-∂T|>3.0×10^-4N/m² the influences of vaporiza tion heat loss on the temperature distribution and its maximum temperature are very small and can be neglected.