Abstract: Against the backdrop of global carbon emission reduction, ammonia is receiving increasing attention as a cheap, safe, easy-to-store and transport zero-carbon fuel. Utilizing ammonia to replace coal combustion for power generation is an important way to reduce carbon emissions. The combustion characteristics of ammonia with low calorific value, slow combustion rate and high NO_x emission are the difficulties that need to be faced when blending ammonia in coal-fired boilers. In this paper, the experiment of coal-ammonia co-firing under the condition of deep air classification was carried out in a two-stage drop tube furnace reaction system. The effects of temperature, separated secondary air ratio and ammonia blending method on the combustion characteristics of coal-ammonia co-firing were studied. The experimental results show that when ammonia is added to the primary air, NO emissions increase monotonically with temperature, and sharply increase after 1200 ℃. NO first decreases and then increases with the increase of the separated secondary air, and the optimal separated secondary air ratio is around 30%. When ammonia is added to the separated secondary air, due to the SNCR effect of NH₃, NO emissions are lower below 1100 ℃, which is comparable to pure coal combustion under low co-firing conditions. As the separated secondary air ratio increases, NO emissions first decrease and then increase, and the optimal separated secondary air ratio is 20%. Experimental results have shown that appropriate air distribution can control the NO emissions of coal ammonia co combustion with a co combustion ratio below 20% without increasing the ratio of pure coal combustion, and the CO emissions and fly ash carbon content are lower than those of pure coal combustion. Therefore, NH₃ can be used as an alternative fuel to reduce CO₂ emissions from coal-fired power plants.