Abstract: As known to all,to improve the fatigue strength of welded joints,it is necessary to polish the weld toe.Recently it has been found that the fatigue life of welded joint can be increased dramatically by ultrasonic peening the weld toe.In this paper,a ultrasonic peening device based on piezoelectric ceramic transducer is firstly developed successfully.This equipment is convenient because of its small size、light weight、low power consumption as well as other merits.In order to study the effectiveness of peening treatment with the equipment,the fatigue tests has been carried out in Q235 steel.The results show that the fatigue life of the peened joint is 20~30 times as long as the as-welded joints.Therefore,the improvement of the fatigue strength of welded joints by ultrasonic peening is remarkable.It is seen that the weld defects such as shallow cracks and slags at the welded toes can be removed effectively during the ultrasonic peening process.That is a reason for improving the fatigue strength of welded joints with this technique.