We used commercial activated coke (AC) as adsorbent and fixed-bed, FTIR, N2 adsorption, ion chromatograph as research methods to study the SO2 removal mechanism in the presence of O2 and H2O and adsorbate (H2SO4) desorption mechanism by combined regeneration. The results showed that AC saturation sulfur retention (52.6 mg/g) in SO2+O2+H2O atmosphere was 4.6 times as much as that (11.4 mg/g) in SO2+O2 atmosphere and 5.0 times as much as that (10.6 mg/g) in SO2+O2 atmosphere at 90 oC. O2 and H2O were necessary in AC desulfurization process. Reaction of SO3 and H2O (g) and condensation of sulfuric acid vapor were the dynamic of AC desulfurization process. Water vapor blowing in combined regeneration inhibited the reaction between H2SO4 and carbon, and consequently reduced the chemical lost of carbon. AC cumulative quality loss (53.6%) of five-times in C-R was still less than that (62.4%) of three-times in H-R. Water vapor blowing inhibited reactivation effect, as a result reducing the changes of AC pore structure and surface functional groups. Adsorbate H2SO4 generated in desulfurization evaporated to sulfuric acid vapor due to the high temperature in regeneration and was carried out by water vapor.