Abstract: To explore the toxic effect of Cd²⁺to Microcystis Aerugionosa, the laboratory test was conducted to study its physiological and chemical changes under different levels of Cd^2+. The results show that: (1) Cd^2+has significant toxic effects on Microcystis aerugionosa, the 24h-EC50、48h-EC50、72h-EC50、96h-EC50 are 0.978, 0.863, 0.646 mg/L and 0.302 mg/L respectively, and EC50 significantly reduces with time (P<0.05);  (2) Under the stress of Cd²⁺, the photosynthetic physiological characteristics of Microcystis aeruginosa are affected, the chlorophyll fluorescence characteristics Fv/Fm, Y［II］, ETR, qP trends to be consistent with chlorophyll a and shows a dose-response relationship; (3) Cd²⁺induces oxidative stress, in which MDA content and SOD activity are significantly increase (P<0.05), and with prolonged exposure, the oxidative stress intensity increases. Therefore, it is concluded that Cd^2+could inhibit the growth of Microcystis aerugionosa, hinder photosynthesis and cause oxidative stress.