Selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) is an efficient NO x abatement strategy, but deNO x catalysts suffer from serious deactivation due to the coexistence of multiple poisoning substances such as K, SO2, etc. in the flue gas. It is essential to understand the interaction among various poisons and their effects on NO x abatement. Here, we unexpectedly identified the K migration behavior induced by SO2 over K-poisoned FeVO4/TiO2 catalysts, which led to alkali-poisoning buffering and activity recovery. It has been demonstrated that the K would occupy both redox and acidic sites, which severely reduced the reactivity of FeVO4/TiO2 catalysts. After the sulfuration of the K-poisoned catalyst, SO2 preferred to be combined with the surface K2O, lengthened the K–OFe and K–OV, and thus released the active sites poisoned by K2O, thereby preserving an increase in the activity. As a result, for the K-poisoned catalyst, the conversion of NO x increased from 21 to 97% at 270 °C after the sulfuration process. This work contributes to the understanding of the specific interaction between alkali metals and SO2 on deNO x catalysts and provides a novel strategy for the adaptive use of one poisoning substance to counter another for practical NO x reduction.