The invention relates to a large-net-clearance self-resetting steel frame center bracing system with a flange plate, and belongs to the field of structural engineering. The diagonal bracing system isan assembled buckling-restrained Y-shaped brace, an energy dissipation element is arranged at a diagonal bracing position, the overall stability and structural lateral load resistance of the diagonalbracing system are improved, a door opening can be formed in the position of the brace, so that the design form is more flexible, and different structural forms can be met. By adding a novel combinedself-resetting device, the overall bearing capacity of a beam can be improved, over-stress load applied to an I-beam section caused by pulling cable pretension in the combined self-resetting device can be avoided, pre-stressed cable pretension is applied, so that the structure can control development of plastic deformation and damage accumulation, and the structure has good anti-seismic property and resetting capacity. All components of the system are machined by a factory and mounted in a connected manner by the aid of high-strength bolts, high requirements for component machining precision and quality can be easily met, rapid assembly is easily realized.