Abstract: An improved method for optimizing ammonia injection in SCR denitrification system was proposed in this paper. The ammonia injection grid is initially adjusted based on the nitrogen oxide mass distribution at the SCR inlet, and then secondary adjustments are made based on the nitrogen oxide mass concentration distribution at the SCR outlet. Based on this optimization and adjustment strategy, experiments were conducted on a 600 MW coal-fired unit. The results showed that the uniformity of nitrogen oxide mass concentration distribution on both sides of the SCR outlet under 100% load conditions was significantly improved, with the relative standard deviation decreasing from 56.4% and 69.1% to 12.0% and 11.6%, the ammonia supply flow rate decreasing by 28.8% and 26.9%, and the average ammonia escape concentration at the SCR outlet decreasing from 3% μ L/L drops to 1.3 μ L/L, ammonia escape peak from 4.5 μ L/L drops to 1.6 μ L/L, eliminates the phenomenon of excessive local ammonia spraying, and the experimental effect is significant.