The direct conversion of SO2 to SO3 is rather difficult for flue gas desulfurization due to its inert dynamic with high reaction activation energy, and the absorption by wet limestone-gypsum also needs the forced oxidation of O2 to oxidize sulfite to sulfate, which is necessary for additional aeration. Here, we propose a method to remove SO2 with highly synergistic H2O2 production based on a novel dual-function photoelectrocatalytic (PEC) system in which the jointed spontaneous reaction of desulfurization and H2O2 production was integrated instead of nonspontaneous reaction of O2 to H2O2. SO2 was absorbed by alkali liquor then oxidized quickly into SO42- by a nanorod α-Fe2O3 photoanode, which possessed high alkali corrosion resistance and electron transport properties. H2O2 was produced simultaneously in the cathode chamber on a gas diffusion electrode and was remarkably boosted by the conversion reaction of SO32- to SO42- in the anode chamber in which the released chemical energy was effectively used to increase H2O2. The photocurrent density increased by 40% up to 1.2 mA·cm-2, and the H2O2 evolution rate achieved 58.8 μmol·L-1·h-1·cm-2 with the synergistic treatment of SO2, which is about five times than that without SO2. This proposed PEC cell system offers a cost-effective and environmental-benign approach for dual purpose of flue gas desulfurization and simultaneous high-valued H2O2 production.