Allelopathic inhibition activities of four submerged macrophytes (Potamogeton maackianus, Vallisneria spiralis, Elodea nuttalli & Ceratophyllum demersum) on Microcystis aeruginosa are investigated by a series of experiments in a short-term bioassay.Individual algal test reveals culture solution of P.niaackianus and C.demersum have better effects on algal growth inhibition.Fur-therrnore, continuous addition assays show strong growth inhibition by culture solution.Inhibitory activity is different in aquatic extracts from different section of P.maackianus.Removing the disturbance of microorganism by autoclaving influences algal assay.These results provide that unstable and excreting continuously allelopathic compounds by submerged macrophytes are the primary cause of algal growth inhibition.Interference with algal growth experiments was investigated in microorganism and nutrient elements of nitrogen and phosphorus.