the inhibitive effects of three terrestrial Compositae plants, Artemisia lavandulaefolia, Conyza Canadensis and Chrysanthemum morifolium on the blue algae were compared by co-cultivation with Microcystic aeruginosa. Results showed that Artemisia lavandulaefolia and Conyza canadensis accommodate to water cultivation，Artemisia lavandulaefolia and Chrysanthemum morifolium (rotted during the last three days) had the most inhibitive potential, with the inhibition ratios to algae (inoculation concentration 2.0×106 cells/ml) is 93.3% and 90.8% respectively, to algae (inoculation concentration 4.0 106 cells/ml)is 89.3% and 79.2% on the 10th day. The active compounds from dry powder of Artemisia lavandulaefolia were extracted by three kinds of organic solvents with different polarities and all the three extracts (solvents removed) had significant inhibitive effect. Among them, ethyl acetate extract was the strongest, with 0.83g/L extract that will reach up to 100% inhibition ratio by calculation. Result showed that A. lavandulaefolia, which grew well in the aquatic environment, might have a great potential to be applied to treat algae bloom and control the eutrophication of water.