Abstract: The extraction condition of polysaccharide from cordyceps militaris by subcritical water was optimized using the single factor and response surface methodology and composition analysis and determination of antioxidant activity of polysaccharide from cordyceps militaris were studied. The results showed that the optimum extraction parameters obtained from response surface analysis were as follows: the ratio of polysaccharide in the extracts was 7.13% at p H value 8,180 ℃ for 13 min with the liquid- solid ratio of 21∶ 1( m L / g).Compared with the traditional hot water extraction,subcritical water extracting polysaccharide from cordyceps militaris had obvious advantage in saving time,extraction ratio( the methods of alkaline water was 7.13%,180 min).Cordyceps militaris polysaccharide by traditional hot water extraction and subcritical water extraction had certain reducing power and the role of the DPPH· clearing IC₅₀ value concentration were 0.324 mg / m L and 0.314 mg / m L.Infrared spectrometry analysis showed that polysaccharide from cordyceps militaris by hot water extraction and subcritical water extraction had the same structure features.