The invention relates to a process method for producing an inclined vertical rib structure rotor support frame center body of a large-scale vertical generator. The process method comprises the steps of center tube formation after center tube and upper and lower annular plate stock preparation, split welding after center tube formation, inner and outer surface processing and narrow gap submerged arc welding divided edge processing. The center tube, a rib plate and the upper and lower annular plates are assembled, a combined body of the center tube and the upper and lower annular plate is hoisted onto a rolling wheel frame. Welding seams between the center tube and the upper and lower annular plates are welded by a welding method of the narrow gap submerged arc welding. The process method belongs to the significant improvement on the manufacture technology of the inclined vertical rib structure rotor support frame center body of the large-scale vertical generator. The workpiece size stability and the manufacture quality are greatly improved. The process method has the advantages that the operation is easy, the welding cost is low, at least a half of the manual cost is saved, the production period is saved by 76 percent, and the production efficiency is improved by about 4.17 times.