In order to study the heterogeneous oxidation mechanism of SO₂ on γ-Al₂O₃ (110) surface by HONO, the authors calculated the adsorption and oxidation mechanism of SO₂ and HONO on γ-Al₂O₃ (110) surface by the first principles based on density functional theory (DFT). The results showed that SO₂ was adsorbed on the perfect/defect γ-Al₂O₃ (110) surface in the form of molecules, while HONO existed only on the perfect surface in the form of molecules. The existence of oxygen vacancies on the surface not only enhanced the adsorption strength of SO₂ and HONO, but also induced the decomposition of HONO on the oxygen defect surface (HONO→NO + ·OH). The analysis of partial density of states (PDOS) and Mulliken charge distribution showed that the decomposition of HONO follows the Haber-Weiss mechanism. It is found that SO₂ and HONO were adsorbed on the oxygen defect surface, and the OH radicals generated by HONO decomposition oxidized SO₂ to form HOSO₂ cluster molecules. This study not only helps to understand the role of HONO in the oxidation of SO₂ on the surface of mineral oxides, but also provides a theoretical basis for explaining the formation of atmospheric sulfate aerosols.