The mechanism of adsorption and oxidation of Hg⁰ by HCl on γ-Fe₂O₃ surface was investigated by density functional theory (DFT) calculation. The adsorption models of Hg⁰, HCl, HgCl and HgCl₂ on γ-Fe₂O₃(001) surface were constructed, and the reaction mechanism of catalytic oxidation of Hg⁰ by HCl on γ-Fe₂O₃ surface was analyzed. The results illustrate that the Hg⁰ tends to be chemically adsorbed at Fe_oct site. HCl can be dissociated and adsorbed on the surface of the catalyst to form adsorbed Cl and hydroxyl groups, and promote the adsorption of Hg⁰. HgCl can be molecularly chemisorbed upon γ-Fe₂O₃(001) and act as an intermediate. HgCl₂ tends to be adsorbed in parallel on the surface of γ-Fe₂O₃. HCl oxidizes Hg⁰ on γ-Fe₂O₃(001) following the L-H mechanism: chemically adsorbed Hg⁰ reacts with dissociatively adsorbed HCl. By measuring the energy distribution of the reaction path, the oxidation process of Hg⁰ on the surface of γ-Fe₂O₃ was studied. The heterogeneous oxidation of Hg⁰ by HCl proceeds on a two-step reaction pathway: Hg⁰(ads)→HgCl(ads)→HgCl₂(ads).