Abstract: As a typical box-shaped container circular flange-plate-shell structure which has a closed weld, the welding deformation characteristics, deformation mechanism and control measures are studied. The actual test and finite element results show that the flange circumference area produces different degrees of inward deflection and collapse-deformation after welding. Under the trend of angular deformation of circular fillet weld, the inclination deformation of the panel near the annular weld area is the direct cause of collapse-deformation, and further collapse-deformation in the annular area of the panel caused by circumferential contraction of annular fillet weld after welding results in inwards deflective and unstable deformation and collapse-deformation of the flange. The deformation control measures with setting the close contact and enough size of the ring temporary reinforcement plate on the inside of the low stiffness panel below the circumferential weld can reduce the collapse-deformation and roundness of flange after welding by 60% compared with the original data, welding deformation is effectively controlled.