Abstract: This paper investigated dynamic changes of total flavonoids in Solidago canadensis L. to exploit this plant at the best time. NaNO2-Al (NO3)3-NaOH colorimetry assay and HPLC was used to determine total flavonoids concentration and ingredients, respectively. The results showed that all parts of Solidago canadensis L. contained total flavonoids. During its germination peak from April to June, total flavonoids concentration increased apparently and maximized in June in leaves, while it dropped gradually in branches and stems, roots and rhizomes. In this period, flavonoid ingredients were lower in all organs, which were mainly chlorogenic acid and caffeic acid. After July, total flavonoids concentration in leaves dropped and minimized in October. In branches and stems, roots and rhizomes, it increased after July and maximized in September and October, respectively. From July to August, flavonoid ingredients were with the most types including flavonoid glycosides, especially quercetin glycosides in all organs compared with other months. In Octobor, flavonoid ingredients in leaves decreased apparently. Therefore, collection of flavonoids from Solidago canadensis L. during its germination peak and hot summer could make full use of the plant and control its further expansion. The flowers could also be collected for total flavonoids after its anthesis in October．

Key words: total flavonoids, flavonoids concentration, flavonoids ingredient, Solidago canadensis L.