Objective: To investigate the dynamic change of flavonoid fractions in different harvesting period of Scutellariae baicalensis that use the content ratio of 19 kinds flavonoid fractions for the standard. And it can define the optimal harvesting period of medicinal materials. At the same time it can find the best Scutellariae baicalensis to provide basis for the standard of clinical medication. Method: A gradient mobile system was applied in the experiment. The HPLC separation was performed on a C18analytical column gradient eluted with acetonitrile-0.1%CH3COOH

detection wavelength was set at 276 nm

at the flow rate of 1.0 mL·min-1

the temperature of column was maintained at 25℃ and use the area normalization method for data analysis. Result: The content ratio of flavonoid fractions is different form a year to three years between spring and fall. Conclusion: The method provide reliable scientific basis for the the optimal harvesting period and quality control of S. baicalensis.