Abstract: The effects of ultrasonic impact treatment(UIT) on the residual stresses of welded rectangular steel(Q345) pillar were investigated.Submerged arc welding(SAW) and electroslag welded joint are processed with UIT.Two impact methods,full impact and weld toe impact,are involved for SAW joint.The test results indicated that UIT can produce compressive stress under the weld(depth less than 3 mm) and the max stress reaches-134 MPa.Weld toe UIT can reduce the residual stress of the toe and the weld.The measurement of residual stress on partial penetrating and penetrating SAW shows that,within the depth of stress measuring(drill-hole method),the UIT can reduce the maximum principal stress of the weld by 34% to 55%.