Abstract: Ammonia is an ideal carbon-free fuel, and it is an effective measure to reduce carbon emission by reducing part of coal fuel in coal-fired power generation through ammonia-coal co-firing. The high nitrogen characteristics of ammonia have attracted increasing attention to the NO emission during the ammonia-coal co-combustion. It is worth mentioning that the airflow velocity affects the flow field distribution and significantly affects the generation of NO in the co-combustion process. Based on this, a high-temperature tube furnace is used to study the influence of air velocity change on the NO generation characteristics of ammonia-coal co-combustion, and the research temperature and ammonia mixing ratio range are 1000−1500 ℃ and 0−20%, respectively. The results show that the decrease of gas velocity can enhance the combustion of ammonia and coal volatiles, and increase the peak concentration of NO. In the temperature range from 1200 ℃ to 1500 ℃, the increase of airflow speed improves the conversion rate of fuel-N, resulting in a higher conversion rate of fuel-N when the crucible aperture d is 1.8 mm compared to when the crucible aperture d is 2.0 mm. With the increase of gas velocity, the fuel-N conversion of ammonia-coal mixed combustion at high temperature is higher than that of pure pulverized coal combustion.