The aim is to modify the activated carbon from sewage sludge with γ-Al2O3 by sol-gel, investigate its performances on the SO2 adsorption and the desulfurization mechanisms in the presence of gaseous oxygen. The modification of the activated carbon from sewage sludge was carried out by adding γ-Al2O3 to improve the SO2 adsorption in a simulated flue gas. The results indicated that γ-Al2O3 porous membranes addition was very effective in promoting the BET area and pore volumes of the activated carbon from sewage sludge. γ-Al2O3 porous membranes in the presence of gaseous oxygen had much effect on the adsorption performance and benefited the SO2 adsorption capacity. The physically adsorbed adsorption took place first. And the following reactions should be occurring on the active sites (*) because of the specific pore construction, BET area and surface functional groups on γ-Al2O3/activated carbon from sewage sludge: (1)SO2 + *→SO2* , (2) O2 + *→O2* , (3)SO2* + O2* → SO3* , (4) 3SO3* + Al2O3 → Al2(SO4)3.