Abstract: Cadmium is highly toxic to plant growth. It causes toxic effects on primary producers in water. The physiological and biochemical characteristics were investigated when Chlorella vulgaris was exposed to different concentrations of Cd²⁺. The results showed that the contents of protein, soluble sugar and chlorophyll in C. vulgaris cells increased under 5—40 μmol/L of Cadmium, and were slightly higher than those of the control group when the concentration reached 30 μmol/L; however, they all gradually decreased when the Cadmium concentration was higher than 30 μmol/L. The SOD activity and H₂O₂ content increased firstly, and then decreased, which reached their peaks at 35 μmol/L. The content of MDA increased with the increase of Cd²⁺ concentration. These results indicated that C. vulgaris can respond positively to the heavy metal cadmium stress to keep their normal growth and metabolism.