Abstract: The evolution processes of arc welding plastic strain in mild steel,stainless steel and titanium alloy thin plate were analyzed by using numerical simulation method,respectively.Comparing with the measurement results,the calculation results demonstrate that both of longitudinal and transverse plastic strains in the weld and near weld zone during the welding process are compress plastic strain.The tensile unloading generated in the cooling stage cannot compensate the pre-existing compress plastic strain,which makes the residual plastic strain in the weld and near weld zone remain in compressive state.The width of compress plastic strain area is obviously wider than that of"materials' mechanics melting zone".Welding speed has a significant effect on residual plastic strain and stress in titanium alloy plate.