According to the design requirement of airflow uniformity of SCR denitration device in a power plant, established a three-dimensional model with a ratio of 1:1 and simulatedwith CFD after meshing. On the basis of the simulation result, contrasted and analyzed five parameters of speed relative standard deviation, the max flue gas incident angle, the temperaturemaximum absolute deviation, the molar ratio of NH3/NO and the systempressure loss, and investigated the guide plate optimal setting rule in the key positions. The results showed that in the SCR denitration system, it is necessary to set the equidistant guide plate at the flue entrance for uniform airflow into rear pipe, and the guide plates should also be set at the appropriate positions with reducing and changing direction to prevent the gas flow to one side. The guide plate size and the flue pipe shape nearest to the reactor have the most impact on the airflow uniformity. Installing the little pipe on the reactor top would improve local position air uniformity.