Using Box-Behnken central combination test design and single factor test were used to optimize the fermentation process of cordyceps polysaccharide, water extraction and alcohol precipitation process and deproteinization process. The results showed that the optimum fermentation conditions of Cordyceps tenuipes were glucose 33.3 g/L, peptone 29.2 g/L, inoculation amount 3.9%. The optimum extraction conditions of Exopolysaccharides were concentration, 3 times ethanol, pH 6.0 and precipitation for 24 h. The optimum extraction conditions were 1∶40 (g/mL), extraction time 90 min, extraction times 2 times, and extraction temperature 80 ℃. In the purification of polysaccharides, the optimum deproteinization techniques of Sevage were as follows: the volume ratio of chloroform to n-butanol was 4∶1, the volume ratio of Sevage reagent to fermentation broth was 1∶2, the shaking time was 15 min, and the deproteinization times was 3 times. After optimization, the yield of extracellular polysaccharide increased by 37.89%, that of intracellular polysaccharide increased by 24.59%, and the protein removal rate was more than 75% after purification.