This study aimed to investigate the evolution of sulfur species on titanium ore, Fe2O3, and TiO2 modified activated coke (i.e., TOAC, FeAC, and TiAC) during the flue gas desulfurization process. The results showed that TOAC, FeAC, and TiAC displayed better desulfurization performance than a blank sample, with the highest sulfur capacity for TOAC at 209.4 mg g(-1). With desulfurization time, the ratios of the adsorbed-S and other-S on activated coke decreased gradually, while those of the water-soluble sulfate increased significantly. The water-soluble sulfate was the main desulfurization product, which accounted for 66.1%, 78.4%, and 76.6% of total removed SO2 for FeAC, TiAC, and TOAC at breakthrough time, respectively. The production of water-soluble sulfate could be related to the decrease of C=O groups and the increase of C-O groups. Meanwhile, the produced water-soluble sulfate covered the active sites (i.e., functional groups, TiO2, and Fe2O3) on activated coke, resulting in the decrease of the adsorption and oxidation of SO2. Higher sulfur capacity of TOAC could be attributed to the synergistic effects between Fe2O3 and TiO2 on TOAC. TiO2 can serve as an oxygen carrier and promote the transfer of oxygen molecules to oxidize SO2, while Fe2O3 was transformed into Fe-2(SO4)(3).