In this study, the deactivation of commercial V₂O₅-WO₃/TiO₂ selective catalytic reduction catalysts by Pb was discussed primarily, and the combined promotive effects of SO₂ and HCl on Pb-poisoned V₂O₅-WO₃/TiO₂ catalysts were studied. The results show that the treatment with SO₂ and HCl markedly improves the NO_x conversion of Pb-poisoned catalysts. SO₂ and HCl react with Pb chemisorbed on V₂O₅, which increases effectively the ratio of V⁵⁺ and active oxygen species and the amount of acid sites.