The article focused on the example of a 170 ℃ low-temperature SCR denitrification project for lime rotary kiln flue gas. The system had been running continuously for 6 months, and there had been a decrease in denitrification efficiency and catalyst deactivation. In order to find the cause of deactivation and solve the problem, BET specific surface area, ammonium radical mass ratio, SEM-EDS, XRF detection were conducted on the catalyst module. SEM photos showed that there was no physical damage to the appearance of the catalyst; The decrease in BET specific surface area of the catalyst indicated that the attachment covers the pore structure of the crystal surface; The ammonium radical mass ratio in the catalyst increased, and EDS and XRF detected an increase in the mass fraction of SO₃ content in the catalyst. It was inferred that the main component of the catalyst attachment was ammonium sulfate. After heat treatment of the catalyst, the BET specific surface area was increased, indicating that heat treatment could effectively remove surface attachments on the catalyst. Using high-temperature flue gas at around 950 ℃, mixed with lime rotary kiln flue gas at around 170 ℃, the flue gas was heated to 380 ℃, and the catalyst was subjected to continuous 48 hours of heat treatment. The results were indicated that heat treatment could restore the catalyst denitrification activity, and all indicators of the SCR denitrification system could be restored to normal operating conditions, effectively solving the problem.