Abstract: According to the characteristics of welding process, this paper divided the welding joint of a weldment into three zones:the liquid zone in the molten weld pool, the solid-liquid co-existing zone and the solid zone. In order to develop the stress-strain numerical model, the mechanical behaviors of the three zones were analyzed in detail. Moreover, Based on the solid fractions during solidification process and loading-unloading deforming curves of stainless steel SUS310, this paper also studied the effects of deformation of welding pool, the rheologic properties and solidification shrinkage on stress-strain evaluating processes. Finally, the influence of the deformation in the molten-weld pool was eliminated by element rebirth method. Furthermore, the algorithm of the thermal stress/strain for the solid metal formulated on the basis of the incremental thermo-elastoplastic constitutive theory. As a result, a numerical simulation model of stress-strain distributions for welding solidification crack was developed.