Abstract: The effect of ultrasonic impact treatment（ UIT） on the welding residual stress,microstructure and hardness in Q460 high-strength steel welded joint was investigated. The investigated results show that UIT can effectively reduce the surface welding residual stress,and the tensile stress on the surface is turned into the compressive stress after UIT. In addition,UIT can eliminate the pits and sharp corners in the weld toe region,which results in smooth transition region between the weld toe and the base metal. Furthermore,grains in the surface are refined after UIT and the depth of the refined grain layer reaches up to 120 μm. Moreover,the surface hardness is increased by 40 HV0.2 after UIT and the depth of hardened layer is about 2 mm.