Objective: To analyze sources and residue accumulation dynamic change of SO2 in Ophiopogonis Radix for providing a theoretical basis to solute problem that SO2 residue in Ophiopogonis Radix exceeded the standard. Method: Twenty-eight medicinal materials of Ophiopogonis Radix were collected

which were processed with different methods in main producing area of Sichuan.Residue of SO2 in samples were measured.Based on measurement results and after processed by coal fire baking and smouldering sulphur

residue accumulation dynamic change of SO2 in Ophiopogonis Radix were investigated. Result: Residue of SO2 in 28 samples exceeded the standard with rate of 35.71%.Sources of SO2 residue were coal fire baking and smouldering sulphur.SO2 residue was in direct proportional to baking time.Marginal time of SO2 residue out of the limit was 8-10 h.SO2 residue was also in direct proportional to smoked sulfur time and material moisture content.SO2 residue reached up to 1 017.69 mg·kg-1 when fresh Ophiopogonis Radix was processed with smouldering sulphur for only 1 h. Conclusion: Consider of quality and medicine safety of Ophiopogonis Radix

it should be forbidden with smouldering sulphur and control baking time strictly in processing of Ophiopogonis Radix.