Abstract: The activity of two kinds of antioxidized enzymes and the content of Chla in Microcystis aerugiuosa Kütz was studied with treatment of nitric oxide under high light.The results showed that the activity two kinds of anti oxidized protections enzymes ASA-POD and SOD has been obviously enhanced under high light.Fluorescence parameters(Fv/Fm) was decreased 90% under high light after treated with nitric oxide,but it restored normally after 6 h.So Chla content was protected by nitric oxide under high light.