Abstract: By means of macroscopic analysis, physical and chemical testing, SEM and EDS analysis, the failure cause of the air preheater seal of a fuel power plant was analyzed. The analysis results show that the air preheater seal was regularly damaged, which was caused by low-temperature sulfuric acid dew point corrosion, seal scraping, and soot-blowing steam with water. Among them, the soot-blowing steam with water was the primary cause for the failure. It is suggested to improve the quality of soot-blowing steam by increasing its superheat degree and prolonging its hydrophobic time. In this way, the damage of the seals can be slowed down.