Abstract: In this study, A. villosum was used as the raw material, and 0.1 mol/L NaOH alkaline solution was used as extraction solution to prepare A. villosum polysaccharides. The composition, structure and antioxidant activity in vitro were analyzed. The results showed that, the extraction rate of polysaccharides was 3.97%, the total sugar content was 37.10%, the uronic acid content was 65.66%, the protein content was 4.36%, and the molecular weight of polysaccharide was 95.46 kDa. The results of high-performance liquid chromatography showed that A. villosum polysaccharides were mainly composed of arabinose, xylose, galactose and galacturonic acid. Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), X-ray diffraction(XRD), thermogravimetric analysis(TGA) results showed that it was an amorphous structure, had a pyran ring, and thermally stable sheet-like acidity heteropolysaccharides. The results of in vitro antioxidant models(DPPH, ABTS⁺, hydroxyl free radicals) showed that the polysaccharides of A. villosum had good in vitro antioxidant capacity. This research aimed to provide a theoretical basis for the application andproduct development of polysaccharides from A. villosum.