Manganese-based catalysts supported by TiO₂ (MnO₂/TiO₂) show good deNO_x performance at low temperature. However, the microscopic impact mechanism of poisonous substances such as K and SO₂ on the deNO_x of the MnO₂/TiO₂ catalyst is a grey area. In this work, the poisoning mechanism of K and SO₂ coexistence on the deNO_x of the MnO₂/TiO₂ catalyst was explored by using a density functional theory combined with experimental methods. SO₂ has low adsorption performance on the MnO₂/TiO₂ (001) surface, while it can be oxidized to form SO₃, and it will react with the catalyst to form sulfates. K poisoning makes NH₃ and NO molecules more difficult to be adsorbed on the MnO₂/TiO₂ (001) surface. However, when SO₂ is introduced on the catalyst surface with K poisoning, it can interact with K and change the charge transfer from K to the catalyst surface, alleviating the K poisoning of the catalyst. These results contribute to the understanding of the mechanism of K and SO₂ co-poisoning on the deNO_x of Mn-based catalysts at a microscopic level, and provide guidance for designing Mn-based catalysts with high anti-poisoning ability.