A new technology for manufacturing large sealing flange is presented. It involves bending combined with welding and finishing machining at the construction site. The innovation in this method is that the preliminary machining of the section, using a heavy-duty vertical lathe, is replaced by precision bending. Therefore large diameter flange can be manufactured at very low cost. Bending of a specimen with an E-cross-section was investigated by numerical simulation and experiment. The mechanism of lateral deformation was analyzed and the method to overcome it was given. This technology was successfully used for manufacturing a large flange which used in a large wind tunnel.