In order to reduce the emission of NO_x and other harmful gases in the process of iron ore sintering and solve the problem of low denitrification efficiency of SCR reactor in a steel mill, a Fluent software is used to numerically simulate the flow field and denitrification reaction process in the SCR reactor, the flow and uniformity of the gas flow in the reactor, the mixing degree of denitrification ammonia and NO_x, and the denitrification efficiency are analyzed, the reasons for the low denitrification efficiency of the SCR reactor are found out, and then the optimization scheme is designed according to the numerical analysis results, and the finite element modeling analysis is carried out on the optimization scheme. The results show that the optimized scheme has a significant rectification effect on the gas, which can improve the uniformity of the gas velocity, reduce the range of the flow dead area above the catalyst layer and close to the reactor inside, and reduce the relative standard deviation of the flow velocity from 29.8% to 7.14%. The uniformity of ammonia gas entering the denitrification tower above the first layer catalyst is improved, and the standard deviation of the ammonia nitrogen concentration ratio is reduced from 22.3% to 4.7%, and the NO removal efficiency is increased from 48% to 73%, which met the requirements of the national emission standard.