Abstract: The liquid fermentation conditions for Stropharia rugosoannulata D5liquid medium in shake flasks were optimized by single factor experiment combined with response surface method,and the antioxidant activity of extracelluar polysaccharides was studied,in order to provide a reference for the production of liquid inoculum and the development of extracellular polysaccharides.The results showed that the optimal liquid fermentation conditions were glucose 30.3 g·L^-1,yeast extract3.7g·L^-1,peptone 1.0g·L^-1,KH₂PO₄2.0g·L^-1,MgSO₄·7H₂O 1.0g·L^-1 and vitamin B₁ 19.0mg·L^-1.The yield of mycelia and extracellular polysaccharides under this fermentation process was 1.317g·（200mL）^-1 and 230.09 mg·L^-1,respectively,which were 37.7%and 15.9%higher than those before optimization.Extracellular polysaccharides was obtained from the fermentation exhibited a strong scavenging effect on Hydroxyl,DPPH and ABTS⁺free radicals,and the scavenging rate increased with the increase of concentration.