Abstract: In order to improve the yield of crude polysaccharide from Chlorella vulgaris and explore the antioxidant effect of purified intracellular polysaccharide from Chlorella vulgaris, this study adopted the method of ultrasonic crushing and hot water extraction to extract intracellular crude polysaccharides from Chlorella vulgaris. Response surface method was used to optimize the extraction conditions. On this basis, anion exchange column and dextran gel column chromatography were used to separate and purify the extracted crude polysaccharides, and the characterization and antioxidant test were carried out. Response surface results showed that the optimal extraction conditions of intracellular crude polysaccharides from Chlorella vulgaris were as follows: The mass fraction of NaOH 2.0%, the material-liquid ratio 1:25 (g/mL), the ultrasonic power 200 W, the ultrasonic time 20 min, the extraction temperature 80 ℃, the extraction time 1.5 h. Under these conditions, the yield of intracellular crude polysaccharide was 18.086%±0.143%. The results of characterization and antioxidant activity in vitro showed that SCIP was a pyranose sugar containing uronic acid and was composed of glucose, rhamnose and galactose. At 20 mg/mL, the DPPH radical scavenging rate was the largest of 75.64%±1.56%, and at 25 mg/mL, the hydroxyl radical scavenging rate was the largest of 71.08%±0.58%. IC₅₀ were 6.42 mg/mL and 8.59 mg/mL, respectively. The results provided a basis for further understanding of the physicochemical properties and biological activities of polysaccharides from Chlorella sp.