Mo/Mn-TiO₂ catalysts were prepared by impregnation method, the effects of reaction temperature, HCl and SO₂ on denitrification and mercury removal from simulated flue gas being studied. The studies showed that, too high reaction temperature was not conducive to the removal of mercury, and too low temperature inhibited the denitrification reaction, but the best efficiency of denitrification and mercury removal can be obtained at 200℃. The addition of HCl can promote the oxidation of mercury, but significantly decrease the rate of NO conversion. The presence of SO₂ in the flue gas played an inhibitory role in the process of denitrification and mercury removal. The catalysts, which before and after the reaction of sulfur poisoning, were studied by XRD, H₂-TPR and XPS. The results showed that the continuous deposition of sulfate on the catalyst surface and the consumption of active component Mn⁴⁺ and chemical oxygen O_α were the main reasons for the deactivation of the catalyst. In addition, the competitive adsorption of SO₂ with NH₃ and Hg⁰ on the surface active sites of the catalyst also severely inhibited the denitration and mercury removal. The denitration process of Mo-Mn/TiO₂ was accomplished by the conversion of Mn valence states, among which both Mo and O₂ were the assistant for the conversion. The removal of mercury by Mo-Mn/TiO₂ was mainly catalytic oxidation, the lattice oxygen in the metal oxide transforms Hg⁰ into HgO and was removed.