As a hydrogen-rich carbon-free fuel,ammonia has the advantages of high energy density,low cost,and safe storage and transportation. Pulverized coal co-firing with ammonia can reduce CO2 emissions during coal combustion. Taking a 20 kW settling furnace (ammonia is injected from the high temperature zone of pulverized coal flame) as the research object,the coupled ammonia combustion characteristics and NO generation law of pulverized coal under deep air classification was carried out. By the numerical simulation,the effects of the ammonia co-firing ratio (0,10%,20%,30%),ammonia combustion zone excess air coefficient (1.08,0.96,0.84,0.72),and the ammonia injection location (0.5，0.6，0.7，1.0 m) on combustion characteristics and NO formation behavior in a 20 kW drop tube furnace with a deep-air staging condition (the ammonia is injected into the high temperature coal-flame zone) were investigated. The results show that compared with pure pulverized coal combustion,pulverized coal co-firing with ammonia increases the carbon content in fly ash and reduces NO emissions. The carbon content in fly ash increases and NO emissions decrease with the further increase of the ammonia co-firing ratio. Considering the combustion economy and NO emissions,the ammonia co-firing ratio with approximately 20% is more appropriate. When the excess air coefficient in the ammonia combustion region is more than 1,the excess of oxygen promotes the reaction of NH3+O2NO+H2O+0.5H2,and amounts of NO are generated. When the excess air coefficient in the ammonia combustion region is less than 1,the incomplete-burning ammonia plays a reducing role,which is conducive  to the reaction of NH3+NON2+H2O+0.5H2,and the formation of NO is inhibited effectively. Considering comprehensively,it is suggested that the excess air coefficient in the ammonia combustion region is maintained at approximately 0.96,which can not only meet the high-efficiency combustion of pulverized coal,but also effectively inhibit the formation of NO during the ammonia combustion process. The farther the ammonia injection location is from the pulverized coal flame zone,the higher the fly ash carbon content and NO concentration is. It is recommended that the ammonia injection location should be as close as possible to the pulverized coal combustion flame zone.