Abstract: In order to understand the residual stress distribution characteristics of typical large-thickness welded structures for nuclear power, and investigate the effect of ultrasonic impact treatment on the regulation of weld residual stress, the surface and internal stress distributions of stainless steel thick plate joints were measured by the XRD method, the hole-drilling method and the contour method, which were used to compare the difference between the weld state and the ultrasonic impact state. Results show that the stress in the top surface and bottom surface of the weld state (the region of 0 and 2 mm) is greater than the internal stress. The measured transverse stress at the weld centerline exhibits a trend of tensile stress-compressive stress-tensile stress from the top surface to bottom surface and the longitudinal stress within the thickness direction is tensile stress. The contour method can realize the overall test of the stress distribution in the thickness direction. The peak value appears at the weld centerline with an 8 mm distance below the top surface and the measured stress is about 420 MPa. Ultrasonic impact treatment has a significant regulatory effect on the surface longitudinal and transverse welding residual stress of the structure, the top surface presents as compressive stress and the internal longitudinal stress at the weld centerline is still maintained tensile stress. The internal transverse stress as the original tensile stress within the region of 1-3 mm is transformed from tensile stress, which reaches 87% of the yield strength of the weld material. However, ultrasonic impact treatment has little effect on the welding residual stress outside of the impact zone.