As a by-product of many combustion processes, NO_x has long affected the environment and human health. In order to reduce NO_x emissions at the source, selective catalytic reduction (SCR) denitrification technology has been widely used due to its high efficiency and mature technology characteristics. However, the alkali and alkaline earth metals generated during the combustion process can adversely affect the SCR catalysts, resulting in a decrease in its denitrification efficiency. Therefore, it is important to study the poisoning mechanisms of alkali metals on SCR catalysts and develop effective anti-poisoning strategies to extend the catalyst lifespan and reduce operational costs. This paper systematically examines the poisoning mechanisms of alkali metals on various SCR catalysts, concluding that alkali metals mainly affect the catalyst performance through chemical and physical poisoning processes. Additionally, an overview is provided on research progress in catalyst modification, rational catalyst structure design, and effective use of catalyst carriers to enhance the resistance of SCR catalysts against alkali metal poisoning. Considering real-world catalyst application scenarios, the paper also explains the joint poisoning effects of alkali metals, SO_2, heavy metals and other components in flue gas on catalysts, while prospecting for future research on synergistic catalyst resistance.