Abstract: Selective catalytic reduction (SCR) denitration process in coal-fired power plants consumes massive amount of ammonia, also generates subsequent problems including ammonia emission and ammonia slip. In-depth study of ammonia emission, such as ammonia slip level and ammonia removal efficiency in the existing ultra-low emission systems of coal-fired power plants can facilitate the formulation of ammonia emission reduction policies and development of ammonia emission reduction technologies. In this study, 14 coal-fired power plants in 11 cities in the air pollution transmission channel of the Beijing-Tianjin-Hebei Region were selected to test the ammonia concentrations at multiple locations of environmental protection facilities. According to the standard test methods such as DL/T 260-2012, ammonia in the flue gas was absorbed by dilute sulfuric acid, and the ammonium concentrations in the solution were determined by spectrophotometry. The results showed that the ammonia emission concentration was low in the chimney, ranging from 0.05 to 3.27 mg/m³, with an average of 0.95 mg/m³. However, the NH₃-slip concentration of 50% units (7 of the 14 units tested) was higher than the design concentration of 2.28 mg/m³, indicating that a common phenomenon that the NH₃-slip concentration of denitration exceeded the design concentration. In some units, serious ammonia slip became a crucial problem. In addition, dry dedusting, wet desulfurization and wet electrostatic precipitator had good ammonia removal ability, with an average removal rate of about 64.86%. For serious NH₃-slip units, it was suggested to carry out network measures of NO_x concentration at the outlet of SCR then conduct refined ammonia spraying and flow field optimization of flue gas to improve SCR denitration operation level (or employ professional operation and maintenance services). These measures can reduce ammonia consumption, reduce system energy consumption and reduce ammonia emissions.