The cost of the Bird's Nest project is 3.8 billion RMB, and the cost after slimming is 3 1 100 million RMB. The external structure of the "Bird's Nest" is mainly composed of huge portal steel frames, with 24 truss columns, 20 truss columns and 2 lower columns have been hoisted. The top of the National Stadium is saddle-shaped, with a major axis of 332.3 meters, a minor axis of 296.4 meters, a height of 68.5 meters at the highest point and a height of 42.8 meters at the lowest point ... On the premise of keeping the architectural style of the "Bird's Nest" unchanged, the new design scheme has greatly adjusted and optimized the structural layout, building cross-sectional form and material utilization rate. The openable roof in the original design scheme was cancelled, the opening of the roof was increased, and the steel consumption was greatly reduced by optimizing the steel structure. The long-span roof is supported on 24 truss columns with an interval of 37.96 meters. The main trusses are radially arranged around the opening in the middle of the roof, and 22 main trusses are straight or nearly straight. In order to avoid too complicated joints, a few main trusses are truncated near the inner ring. A large number of steel structures are box-shaped members welded by steel plates, and the cross-arranged main trusses, together with the substructure of the roof and facade, form a special architectural shape of "Bird's Nest". The main stand part adopts reinforced concrete frame-shear wall structure system, which is completely separated from long-span steel structure.