Abstract: In order to study the best extraction technology of Cordyceps polysaccharide of Cordyceps militaris and its antioxidant function, orthogonal testing [L9(34)] was used to optimize extraction condition for extracting polysaccharide from fruiting body of Cordyceps militaris. Total reducing power, scavenging activity of DPPH and antibacterial capacity of Cordyceps polysaccharide were measured. The results showed that the optimal parameters of ultrasound-assisted hot water extracting Cordyceps polysaccharide were ultrasonic power of 105 W, ultrasonic time of 40 minutes, liquid-solid ratio of 1:25, hot water extraction time of 40 minutes, hot water extraction temperature at 70℃. Yield of polysaccharide was 2.6602% under the optimized condition. Reducing power was the highest when the concentration of Cordyceps militaris was 2.4 mg/mL. DPPH scavenging power was the strongest when the concentration of Cordyceps militaris was 0.45 mg/mL.