OBJECTIVE： To study effective component kinds and content difference of Scutellaria baicalensis with different harvesting periods collected in spring and autumn， and to determine the optimal harvesting time. METHODS： IR-IL was used to analyze the constitutions change of the components in S. baicalensis collected in different harvesting periods （annual， biennial and triennial， in spring and autumn， respectively）. HPLC-MS method was used to analyze the contents change of 6 flavonoids （qroxylin A， chrysin， wogonin， wogonoside， baicalin， baicalein）. RESULTS： Results of IR-TL analysis showed that S. baicalensis contained different components such as flavonoids， glycosides， saccharides， easters in different growth stages， among which the contents of glycosides in biennial S. baicalensis were the highest with more stable quality. The results of content determination of 6 flavonoids showed that different harvesting periods had a great influence on the contents of the above indicators. The overall content of biennial samples collected in spring was higher than that of autumn samples collected in the same year. CONCLUSIONS： This study provides a reliable analytical method for the quality control of S. baicalensis； spring harvest in two-year growth period may be the best harvesting time for S. baicalensis.