Abstract: The die structure and technology of bending of super large mill flange were compared and analyzed. By adjusting the spacing of the support wheels and the height of the limit support, flange bending with different curvature radii can be realized. It is found that there is a gradual separation between the center of the upper die and the surface of the blank during the bending process in trial production, and the evolution from three-point bending to four-point bending is the fundamental reason for the large deviation of the final curvature radius of the bending flange.The key parameters such as the springback and the separation gap of the upper die must be considered in the determination of the reduction amount, and the theoretical value must be compensated and corrected.