Objective:To study the stability of salvianolic acid B powder and aqueous solution. Methods:The determination to content variation in the strong light,high temperature,high humidity conditions and water solution at different temperatures degradation equation by HPLC method and using different concentration of concentrated H₂SO₄ determination of the critical relative humidity.Results:The appearance and content of salvianolic acid B powder did not change under high light,high temperature during the 10 days,and the critical relative humidity of salvianolic acid B powder is 60% under the normal temperature, the Arrenius equation of aqueous solution degradation is IgK=-3.4529/T+7.6408(r=0.9816), K_25℃=1.132×10⁴h^-1,t_0.9=38.80 days.Conclusion:The raw material of salvianolic acid B powder has good stability, water solution less stability.