Abstract: Unreacted ammonia in Selective Catalytic Reduction (SCR) and Selective Non-catalytic Reduction (SNCR) technology may be adsorbed by fly ash and lead to ash blocking in the air preheater or hindering the secondary utilization of ash. Ammonia adsorption by fly ash may have a close relationship to the concentration of ammonia in flue gas. Regarding Ximeng lignite and Yangquan anthracite as the subjects investigated, NH₃ Temperature-programmed Desorption (NH₃-TPD) was utilized to study the relationship between ammonia chemical adsorption and mineral composition of the ash, the atmosphere of ash production, cooling rate of ash as well as the amount of residual carbon in the ash. The results show that rapid cooling and reduction atmosphere could increase the amount of amorphous phase in the ash and facilitate ammonia adsorption. On the other hand, ash with residual carbon could adsorb more ammonia than mineral ash as a result of acidic functional group on the surface of residual carbon.