Abstract: Finite element numerical simulation was applied in the research of ultrasonic impact treatment.With selection of proper loadcase class and contact condiction,a modle of ultrasonic impact treatment was established.The calculation results are in agreement with the experiment results.The results show that tensile residual stresses in the welds of 10Ni5CrMoV steel(R_p0.2 ≥ 785MPa) is 660MPa,ultrasonic impact treatment has significant effects on the residual stress and introduces compressive redidual stress in the welded joints.