Abstract: A denitration project in Zhejiang Huaneng Yuhuan Power Plant in China was taken as the research object, and the finite element method was used to simulate elastic properties in small deformation and large deformation. The mechanical properties of the flue in practical load were studied, and the influence of the flue length on the stress and deformation were discussed. It is found that because of considering large deformation effect, the equivalent stress of the flue is well-distributed, and its values decrease by 5% to 50% The influence of the change in flue length on the stress is less than 20%. At last, monitoring was used to show the reliability of numerical simulation.