This work investigates the corrosion behavior of GH3625 alloy under acidic atmosphere SO2 at 900 ℃. The surface morphologies of the corroded specimens and the corrosion products were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The cross-sectional morphology was examined by SEM, EDS, and electron probe micro-analyzer (EPMA) to observe the internal corrosion. The results demonstrate that the corrosion rate of the GH3625 alloy only slightly increased with increasing SO2 content in the acidic environment. A dense oxide film (primarily Cr2O3) forms on the alloy surface which can effectively prevent SO2 from diffusing into the interior of the alloy matrix. Additionally, chromium inside the matrix can combine with sulfur (primarily CrS) retarding corrosion. GH3625 alloy exhibits excellent corrosion resistance under an SO2 environment.