At present, the development of advanced carbon emission reduction technologies and the realization of the dual-carbon goalshave become the most urgent problems in the energy field. Carbon emissions from coal-fired power plants in China still account for a majorproportion. Ammonia, as a zero-carbon fuel, has significant advantages in heating value, synthesis, transportation and other aspects. Cofiring ammonia in coal-fired boilers is one of the important ways to achieve large-scale utilization, however, the control of nitrogen oxideemissions during large- scale co - firing will be a major challenge in the future. In this paper, the co - firing experiment of ammoniawith coal was carried out in a lab-scale furnace, and the effects of temperature (1 000-1 300 ℃ ), air/ fuel ratio(0.65-1.50), and cofiring ratio(0-30%) on nitrogen oxide emissions were discussed. The results show that the lower combustion temperature and air/ fuel ratiois essential to inhibit the conversion of ammonia to nitrogen oxides. Under the operating conditions of 1.5 air/ fuel ratio and 20% co-firingratio, the NOx emissions reach to 780×10-6 and 1 870×10-6 at 1 200 and 1 300 ℃ respectively. With the increase of ammonia ratio, theNOx emissionsincrease linearly, but the overall conversion of fuel nitrogen to NO decreases significantly. The calculations by detailed chemical reaction mechanisms (e.g. Glarborg 2018, Mendiara 2009, Konnov) show that the prediction results derived by Konnov mechanism are closer to the experimental results. The Konnov mechanism is further used to evaluate the influence of air/ fuel ratio,temperature and other variables on the NO emissions by ammonia combustion. The results show that the temperature and nitrogen oxideemission concentrations increase with exponential rate, while the total NOx emissions change abruptly when the air/ fuel ratio increasesfrom 1.0 to 1.1. A mixing factor is defined to study the effect of the mixing level of oxidant and ammonia on nitrogen oxide emissions, andit is found that prolonging the mixing distance of ammonia and oxidant can significantly reduce the intensity of nitrogen oxide emissions.