Abstract: The weld toe area of a three-time repair welding joint of 30CrMnSiNi2A steel was treated by ultrasonic impact. The effects of the ultrasonic impact on the microstructure, mechanical properties and residual stress of the repair welding joint were studied by microstructure observation, tensile test, hardness test and residual stress test. The results show that the ultrasonic impact caused grain refinement and plastic deformation in the area about 100 μm from the surface of the repair welding joint. The influence of ultrasonic impact on the tensile properties of the welding joints was small because the thickness of ultrasonic impact affected layer was smaller than that of the welding parts. The microhardness of the repair welding joint surface increased significantly by ultrasonic impact, which was related to grain refinement and the increase of dislocation movement resistance on the surface of the repair welding joint. Ultrasonic impact could transform the harmful residual tensile stresses accumulated in multiple repair welding into beneficial compressive stresses.