Abstract: The chemical compositions of Inonotus obliquus were analyzed and crude polysaccharides (IOP)were isolated from Inonotus obliquus by water extraction. The component of polysaccharides were purified by DEAE-52, and Sephadex G-100 column chromatography, and the highly active polysaccharide component was screened out through antioxidant activity, and the purity of the polysaccharide component was analyzed by high-performance liquid chromatography.The experimental results showed that the chemical composition of Inonotus obliquus was rich, including polysaccharide 13.10%± 0.31%, reducing sugar 4.21%±0.40%, protein 2.70%±0.71%, ash 9.60%±0.31%.After IOP undergoes DEAE-52 cellulose column chromatography, four monosaccharide components were obtained: IOP-1, IOP-2, IOP-3, and IOP-4. Antioxidation experiments on four polysaccharide components found that IOP-2 had the highest scavenging rate for DPPH free radicals. After passing through Sephadex-100 chromatography column, IOP-2 obtained two polysaccharide components: IOP-2a and IOP-2b. Compared with its antioxidant activity, the polysaccharide component with higher activity was selected as IOP-2a. Using high performance liquid chromatography to identify the polysaccharide component IOP-2a, only one symmetrical peak was detected, indicating that IOP-2a was a homogeneous polysaccharide.