In order to study the physiological effects of different algal concentrations on their leaves and roots in eutrophic water, the experiment was designed to have 4 treatments, i.e.0,122,166 μg/Land 222 μg/L of Chloro- phyll a, and the physiological indexes between 0 d , 10 d, and 20 d of Vallisneria Asiatica was compared. Re- sults show that the leaves content of soluble protein was inhibited by cyanobacteria, the activity of SOD at 20 d was significantly higher than 10 d，and POD and SOD was inhibited in different degrees in roots. SOD, POD and CAT in leaves of Vallisneria Asiatica had a rising trend with the increase of cyanobacteria concentration to adapt to oxidative stress. MDA increased significantly when the concentration of chlorophyll a (Chl a) was 222 μg/L in water. When the chlorophyll concentration of the cyanobacteria was greater than 122 μg/ L, the plant could adjust its antioxidant defense system to remove the excess active oxygen to adapt to the oxidative stress instead of cyanobacteria concentration. This provides a scientific theoretical basis for controlling cyanobacteria concen- tration in the eutrophic lakes of Taihu and restoring the biological population of Vallisneria Asiatica.