Abstract: To study the reaction mechanism of Hg adsorption by MnO₂-modified activated carbons (C₁₄H₆), the quantum chemistry method MP2 ab initio calculation was used to optimize the 6-311+g(d,p)/SDD basis set to obtain the geometric configuration of the reactants, intermediates, transition states and products, so as to calculate the reaction kinetics. The reaction rate constants at 298-1 500 K and 0.000 1-3 MPa were calculated via transition state theory, and their variation tendency with temperature and pressure was analyzed simultaneously. Results show that in the environment simultaneously containing Hg, C₁₄H₆ and MnO₂, the reaction between MnO₂ and C₁₄H₆ is faster than between Hg and C₁₄H₆, and MnO₂(C₁₄H₆) is easier to react with Hg than C₁₄H₆. The reaction rate constant increases with the rise of both temperature and pressure. The adsorption effect of MnO₂-modified activated carbons for Hg is better than unmodified activated carbons.