The SCR denitration system of sintering machines in ironworks has the characteristics of high flue gas temperature and large flue section size. The structural design method of denitration flue was analyzed. The design of irregular parts such as elbows and stepped pipelines was optimized. The analysis shows that,for the design of irregular parts in denitration flue with small section area, when the center distance calculated by reinforcement ribs was taken as the maximum distance, the reinforcement ribs will be arranged reasonably and the material can be saved. The truss-type inner support structure can increase the section area of flue gas flow and enhance the support stability. For the flue with strong negative pressure,it is necessary to install a deflector to distribute the air flow evenly. From the aesthetic point of view,the reinforcement ribs and inner strut are suggested to be arranged along the track of the deflector. For the flue with large section area, the transverse reinforcement ribs and longitudinal reinforcement ribs should be combined and the reinforcement rib specification should be reduced.