Abstract: Recently years, ammonia (NH₃) has been regarded as the most promising carbon free renewable alternative energy source as a hydrogen rich and carbon free fuel. Co-firing NH₃ with pulverized coal is one of the effective methods to reduce carbon emissions in thermal power generation processes. In response to the emissions of fine particulate matter and nitrogen oxides (NO_x) during NH₃/coal co-combustion, this study conducted NH3/coal co combustion experiments on a two-stage one-dimensional settling furnace. The effects of NH₃ co-firing ratio on fine particulate matter, NO_x emissions, NH₃ escape, and burnout characteristics were investigated during the long residence time of NH₃/coal in the high temperature zone. It was found that the yield of fine particles first increases and then decreases with the ammonia co-firing ratio, and then increases again. When co-firing ratio is 30%, the yield of fine particles reaches its lowest and is lower than that of pure coal condition. In addition, with the increase of co firing ratio, NO_x emissions showed the same trend as the yield of fine particulate matter, while NH₃ escape increased with the increase of co-firing ratio. Besides, with the increase of NH₃ co-firing ratio, NH₃ has a dual effect on the oxidation of CO in the furnace. When the co-firing ratio is below 30%, NH₃ provides additional OH radicals for the oxidation of CO, promoting the oxidation of CO; But after exceeding 30%, NH₃ oxidation consumes too much oxygen, inhibits CO oxidation, and leads to a trend of increasing and then decreasing CO emissions. The gas-phase reaction of NH₃ promotes the devolatilization reaction of coal, strengthens the fragmentation of coal particles, facilitates the development of its pore structure, promotes the oxidation reaction of char, and the unburned carbon content in fly ash gradually decreases with the increase of co-firing ratio. The above results are beneficial for further understanding the emission characteristics of pollutants in NH₃/coal co combustion, and provide data support and theoretical guidance for the development of large-scale coal-fired units with a large proportion of ammonia co combustion technology.