The synthesis of sulfur-doped activated coke (SAC) using SO₂ as an activator enables simultaneous desulfurizer production and sulfur resource utilization. This study systematically investigated the evolution of carbon properties through sulfur doping and the enhanced desulfurization mechanism through experiments and density functional theory (DFT) calculations. The results demonstrated that SO₂ was primarily converted to elemental sulfur (maximum yield: 92.17 %) via redox reactions with carbon, while doped sulfur mainly existed as thiophene and oxidized sulfur groups (maximum doping: 18.92 wt%). Surface sulfur doping modified carbon's physicochemical properties and produced unique saddle-shaped SO₂ adsorption curves. Transient experiments and DFT calculations revealed enhanced hydrophilicity through strengthened H₂O interactions with sulfur-containing groups (the maximum adsorption energy of H₂O reached −58.70 kJ/mol, 2.64 times that of pristine sulfur-free carbon), which promoted H₂SO₄ migration in micropores via concentration-gradient diffusion to enhance desulfurization. This work provided both a waste-to-resource strategy for desulfurizer preparation and atomic-level insights into the desulfurization enhancement mechanism of SAC, offering design principles for advanced carbon materials in flue gas purification.