In order to solve the problem of catalyst wear in the SCR denitrification device of a 660 MW supercritical unit in China to ensure that the denitrification efficiency is not affected, the flow field distribution in the original denitrification device by using the numerical simulation software FLUENT was simulated. Through the analysis of the simulation results, the factors affecting catalyst wear were obtained. Besides, after many simulation tests, the optimization scheme was put forward, and the field test after the implementation of the optimization scheme was carried out. The results show that the flue gas velocity field and fly ash concentration field can be greatly optimized by changing the horizontal flue to a flue with inclined top, increasing or decreasing the number of diversion plates appropriately and changing the distance between diversion plates, so that the efficiency of the SCR denitration system can be improved to a great extent.