Objective To study the influence of ultrasonic impact treatment on microstructure and properties of surface layer of 7A52 alumium alloy welded joint. Methods 7A52 aluminum alloy was welded by double wire MIG welding method. The welded joint was full impacted by UIT-125 ultrasonic impact treatment equipment. Microstructure of the welded joint was observed and analyzed by metalloscope. The mechanical properties of welded joint were tested and studied by microhardness tester and wear testing machine. Results After ultrasonic impact treatment, continuous, uniform and smooth transition arc was formed in weld toe. The stress concentration of welded joints was alleviated. The thickness of surface deformation could reach 25 μm in heat affected zone and 15 μm in base metal. The surface 7A52 aluminum alloy welded joint by ultrasonic impact treatment equipment was obviously strengthened. Denser plastic deformation layer was induced. Surficial grains were refined. The microhardness and wear resistance were significantly increased. Conclusion After UIT, the maximum thickness of surface layer of 7A52 aluminum alloy welded Joint was about 20 μm, and the deformation texture with preferred oriention was formed and parallel to surface of welded joint. Along the thickness direction within 1. 5 mm, the maximum microhardness was 162HV in heat affected zone of the weld zone, 113HV in the weld zone, which were improved by 21. 5% comparing to these without treatment. Moreover, the wear resistance of the surface layer were obviously improved.