Abstract: It's a new method to increase fatigue strength of welded joints and structure by peening toe of weld with ultrasonic peening equipment.In this paper we have researched the ultrasonic peening equipment and a new ultrasonic peening prototype was manufactured.The prototype was fitted with the ultrasonic power supply which can be used specially for ultrasonic peening equipment of the kind of piezoelectric ceramics.The new idea has been held out to keep the output amplitude in constant so as to control the quality of ultrasonic peening.Accurate frequency tracing has not only been realized successfully under the situation that the peening load varies strongly,but the quality and efficiency of the ultrasonic peening and safety of the equipment system has been ensured as well.