Ultra-large cylinder forgings with variable cross-section are key metal components of nuclear island pressure equipment, its diameter and height exceed 5 m and the difference of inner and outer diameters is more than one times which make the overall forming extremely difficult. In order to solve this problem, a new method of profiling forging for ultra-large cylinder with variable cross-section based on the closing process was proposed. The material flow law during the mandrel reaming process was explored. A material deformation analysis calculation model was established to realize the rapid design of the mandrel reaming process for cylindrical parts. The influence laws of different billet shapes on the closing process was explored, and the parameters of closing process were obtained. Based on this, the local forming was adopted to forge the small-sized part into a stepped structure with inner flange. Finally, through the variable diameter mandrel reaming and drawing process, the inner flange structure of forgings was further formed. The feasibility of the profiling forging process scheme for ultra-large cylinder with variable cross-section was verified through scaling experiments.