Abstract: In order to alleviate the problem of ABS blockage in air preheater, taking a 200 MW unit as an example, the study aims to address the problems of large fluctuations in flue gas temperature, high ammonia injection volume, and repeated blockage of air preheater after the unit has been in deep peak shaving state for a long time. Through conducting field tests and combining with historical data from the unit’s DCS, the actual operating conditions of the unit are analyzed to determine the cause of air preheater blockage. Based on the test results, the ammonia injection part of the SCR flue gas denitrification system is optimized and adjusted, eliminating the phenomenon of excessive ammonia injection in the SCR flue gas denitrification system, reducing ammonia escape, delaying ABS generation, and alleviating the problem of air preheater blockage.