Abstract: Through comparative analysis the effect of direct ultrasonic impact, the conventional heat treatment plus ultrasonic impact and vacuum heat treatment plus ultrasonic impact on fatigue life of Q345B steel welded joint were studied, and the mechanism of heat treatment combined with ultrasonic impact on the fatigue property of welded joint was discussed. The results show that conventional heat treatment plus ultrasonic impact compared with ultrasonic impact directly, while the welding residual stress of welded joint is eliminated to some extent, but as a result of material softening lower the impact of compressive stress and surface oxidation raise the risk of forming fold defects, the fatigue performance is reduced, and with the extension of heat preservation time, the fatigue performance decreases more obviously. Although the materials were softened by vacuum heat treatment plus ultrasonic impact, the fatigue life of welded joint was improved compared with that by direct ultrasonic impact without surface oxidation plus residual tensile stress elimination, and the fatigue damage position was transferred from the welding toe to the base material or the welding root.