Abstract: A numerical simulation method was used to analyze the evolution process of arc welded plastic strain in thin stainless steel plates. The calculated results demonstrate that both of longitudinal and transverse plastic strains in the weld and its periphery during welding process were compressive. The tensile unloading generated in the cooling stage could not cancel the pre-existing compressive plastic strain,which made the residual plastic strain in the weld and its periphery remain in compressive state. The width of compressive plastic strain area was obviously wider than that of "mechanics melting zone" in the stainless steel.