Objective Investigate the stability of protostemonine，a characteristic constitution of Stemona japonica, and analyze its changes in the storage and use, and explore the quality control of Baibu materials. Methods Using acetonitrile-water as mobile phase, gradient analysis on HPLC-DAD coupling C18 column was used to compare the changes of protostemonine in trichloromethane, acetone, methanol and other solvents, and to investigate the changes of the characteristic component of Stemona japonica extracted by methanol immersion and water reflux extracts at different storage times. Results In the solvents of trichloromethane, acetone, protostemonine was apt to change into isoprotostemonine, maistemonine and isomaistemonine. However, the transformation was greatly reduced in the methanol solvent. It was observed that the content of protostemonine decreased with the increase of storage time, but the content of maistemonine and isomaistemonine increased. Conclusion The stability of protostemonin was poor, and it was one of the main active components of Stemona japonica, which may lead to the decrease of efficacy of Baibu during storage and use. The quantitative testing standard of Baibu is still needed.