Abstract: In this paper, the migration characteristics of slip ammonia were studied which passed through the various downstream equipments of the SCR system of a 350 MW coal-fired power plant. The field test concludes that the slip ammonia intercepted by the air pre-heater, low temperature economizer, and electrostatic precipitator accounts for 23%~26%, 9%~17%, and 56%~62% of the total slip ammonia, respectively, while that entering the desulfurization system accounts for less than 3% of the total slip ammonia. Raising the temperature of the low temperature economizer outlet flue gas will reduce its capture ratio of ammonia. However, the increase of the ammonia content in the fly ash from the electrostatic precipitator indicates the performance improvement of the electrostatic precipitator for the ammonia capture capability. Therefore, the overall capture ratio remains basically unchanged. Through the field test and data analysis, the relationship between the ammonia content in the fly ash from the electrostatic precipitation and the ammonia escape from the SCR outlet was also established. Nevertheless, whenever there are any significant coal quality changes or equipment modifications, etc., such relationship needs to be revised according to the actual situations.