In order to reduce SO₂ emission in the iron sintering process, the flue gas circulation sintering (FGCS) process has been recommended and put into practice. In this process, flue gas containing low SO₂ concentration is recirculated to the sintering process, achieving the concentration of SO₂ content in the off-gas, which is favorable for current flue gas desulphurization processes. In this study, SO₂ behavior in different sintering zones was investigated under the simulated experimental conditions. In the moisture condensation zone and sinter mixture zone, SO₂ of recirculated flue gas is absorbed by the moisture and slaked lime of sinter mixture; in the drying and preheating zone, part of SO₂ in circulating flue gas is absorbed by dry slaked lime in sinter mixture under low temperature conditions, and SO₂ is generated by oxidization of sulfides and re-released by decomposition of sulphurous acid; in the hot zone, SO₂ in circulated gas is partially absorbed by the molten phases, newly crystallized minerals such as calcium ferrite and dissociative CaO; in sinter zone, part of SO₂ is absorbed by residual CaO in sinter under the condition of humid circulated flue gas, which results in unfavorable increase of residual S in the up layer sinter.