The structure of C plate used for pre stressing frame of large close die forging press was introduced. FEA calculating model of complete machine for close die forging press was set up, the deformation and stress of the combined pre stressing frame with columns each made up of 5 or 6 C plates respectively were compared and calculated. The structure design and manufacture features of C plate used for plate combined pre stressing frame of large close die forging press were analyzed and studied. The combined pre stressing frame with columns composed of 5 C plates was optimized and selected with comprehensive consideration of fabricating process and manufacturing efficiency for C plate. The application is proved by the actual manufacturing and erecting process for the frame of China Erzhong 800 MN large close die forging press.