Ultra-low emission control of nitrogen oxides (NOX) in the cement industry has been continuously tightened, and selective catalytic reduction (SCR) has become the mainstream treatment technology. After the medium-temperature and medium-dust SCR denitrification system of a 5 000t/d cement clinker production line was put into operation, problems such as catalyst clogging, sharp drop in denitrification efficiency and excessive NO_X emission occurred due to the incineration of alternative fuels and co-processing of industrial sludge. In this paper, the technical characteristics of medium-temperature medium-dust and high-temperature hige-dust SCR processes are compared, and the core inducements of catalyst deactivation caused by ammonium bisulfate formation and total organic carbon condensation in the medium-temperature SCR system are analyzed. Aiming at the key technical difficulties of high-temperature high-dust SCR in the renovation, solutions including adjusting the flue gas path, replacing high temperature specialty catalysts, and optimizing the ash cleaning and valve systems are proposed. After renovation, the NO_X emission concentration of the system is stabilized at 36~48mg/Nm³, the denitrification efficiency reaches 88%~92%, the system resistance and energy consumption meet the standards, and the long-term operation stability is significantly improved.