Abstract: Aqueous extracts of 12 kinds of medicinal plants were obtained by soak extraction, and their inhibitory effects on algae growth were studied. The results showed that: when the relative concentration was 1 g·L^-1, aqueous extracts of Stephania tetrandra had the strongest inhibitory effect on the growth of Chlorella pyrenoidosa, and the maximum specific growth rate was -0.28 d^-1. The methanol extract of S.tetrandra had significant and long-lasting inhibitory effect on the growth of C.pyrenoidosa and the lowest effective concentration in inhibiting algae was 30 mg·L^-1.The identification results of HPLC showed that: the main constituents in the extracts were alkaloids such as fangchinoline and tetrandrine, etc.S.tetrandra had great prospect of application in controlling water bloom.

Key words: medicinal plant, water bloom, Stephania tetrandra, Chlorella pyrenoidosa, HPLC