In order to study the welding residual stresses of the butt joint of the U-rib stiffened plate during the on-site assembly of the steel box girder bridge, this paper were designed and fabricated the butt joint specimen of the U-rib stiffened plate during the on-site assembly of the steel box girder bridge. The blind-hole method was used to measure the welding residual stress on the surface of the specimen, and the ABAQUS finite element software was used to simulate the welding of the specimen. The distribution law of the welding residual stress of the specimen model was obtained, and the numerical simulation results were compared with the experimental results. The results show that the longitudinal residual stress are mainly the tensile stresses distributed around the butt weld and near the U-rib fillet weld, and the compressive stresses mainly distributed in the base metal near the outer side of the U-rib and the end of the U-rib fillet weld. The transverse residual stresses are mainly the tensile stress distributed around the U-rib fillet weld, and the compressive stresses mainly distributed at the end of the butt weld.