Abstract: Objective:To optimize the extraction process of Cordyceps militaris polysaccharides and study the protective effect of Cordyceps militaris polysaccharides on oxidative damage of vascular smooth muscle cells. Methods:L₉ (3⁴) orthogonal experiment was used to optimize the extraction parameters of polysaccharides. Hydroxyl radical method, DPPH free radical method and FRAP method were used to test the radical scavenging ability of Cordyceps militaris polysaccharides. The model of cell oxidative damage induced by hydrogen peroxide was constructed at the cellular level. MTT assay and ROS cell staining were used to evaluate the protective effect of Cordyceps militaris polysaccharide on oxidative damage induced by hydrogen peroxide in rat aortic smooth muscle cells. Results:The optimal extraction conditions of Cordyceps militaris polysaccharides were:extraction temperature 90℃, ratio of material to liquid 1:30 g/mL, extraction time 3.0 h, extraction times 3 times, the highest yield was 7.94%±0.16%.The scavenging ability of hydroxyl radicals and DPPH free radicals and total antioxidant capacity at the concentration of 1.6 mg/mL were 75.57%±1.39%, 80.23%±2.75% and (0.22±0.01) mmol/mg, respectively. Cell experiments showed that Cordyceps militaris polysaccharides significantly inhibited hydrogen peroxide-induced intracellular ROS production and increased cell viability. Conclusion:The technology of extracting polysaccharides from Cordyceps militaris was successfully optimized. Cordyceps militaris polysaccharide has good activity of scavenging free radicals in vitro and plays a very good role in prevention and treatment of cardiovascular diseases caused by oxidative stress.