Abstract: Aiming at the specific implementation of the principle of the ammonia injection optimization and adjustment for Selective Catalytic Reduction (SCR) system, a numerical model of a typical SCR system was established by the simulation method to study the regional distribution of NH₃ on the export monitoring section and the pathlines of NH₃ in the device, which was injected by the ammonia sprayed branch pipe. The flue gas velocity and NH₃ concentration at the ammonia sprayed grid area were analyzed under different flue gas volumes. Furthermore, the distributions of NH₃ concentration on the export monitoring section before and after adjustment was compared and analyzed. The results showed that there occurred irregular changes for the positive correspondence between the outlet sections which was evenly divided and the ammonia injection branch pipes, due to the influence of the position of the branch pipe and the structure of the flue. The irregular correspondence increased the complexity of adjusting the amount of ammonia injection of the corresponding branch pipe according to NO_x concentration in a separate area on the outlet section. The pathlines of ammonia sprayed by the lateral partitioned branch pipes were limited in the corresponding region by the deflector structures, while the pathlines of ammonia sprayed by the vertical partitioned branch pipes had a tendency to shift to the one side with the flue gas. Under the condition of the uniform ammonia injection, the relative standard deviations of NH₃ concentration on the section S-2 under the 50%, 75%, and 100% flue gas treatment volume was 19.79%, 19.23%, and 17.17%, respectively, which did not changed significantly due to the changes of the flue gas treatment volume. After optimization adjustment, the relative standard deviations of NH₃ concentration on the section S-2 was 3.8%.