Change of leaf structure, proline and total sulfur content have been study for the banana plantlet treated with SO2 at the different initial concentration level of 0, 1, 2, 5 g/m3. The result showed leaves and leaf cells suffered injury, the total sulfur content and proline content in leaf increased with the increasing SO2 dosage, and protoplasm letting out, cell shrinking, and cytoskeleton damaged. Special unknown red substance produced in cell because of damage by SO2. The results suggested that the production of red substance maybe the only reaction by SO2, and it can be applied for the identification of SO2 pollution as an accessorial tool. The normal growth status when absorb 1.5 times sulfur showed banana plantlet’s decontamination to SO2. The same time, plantlet sulfur content was linear with proline content when treated with SO2.