Abstract: Astragalus polysaccharides are the main immunomodulatory substances in Astragali Radix. The structure of polysaccharides is difficult to accurately determine, which limits the in-depth study of the molecular mechanism of Astragalus polysaccharides in vivo. "Polysaccharide receptor theory" believes that there are one or more oligosaccharide fragment "active centers" in immunologically active polysaccharide molecules. Therefore, the degradation of Astragalus polysaccharides into oligosaccharides and the study of the active centers of polysaccharides at the oligosaccharide level provide new ideas in the study of the structure and mechanism of Astragalus polysaccharides. This article adopts endo-α-1,4-glucanase enzymatic hydrolysis, and determines the best degradation conditions through single factor test and orthogonal test to degrade the immunologically active polysaccharide APS-Ⅱ (10 kDa component) into oligomers with different degrees of polymerization. Then through the preparation of polyacrylamide gel chromatography and specific immune and non-specific immune cell tests, the immune activity screening of different oligosaccharide components is carried out. The animal welfare and the experimental process in this study follow the requirements of the Animal Ethics Committee of Shanxi University. The results showed that compared with the immunologically active polysaccharide APS-Ⅱ, different oligosaccharide components have obvious differences in different immunological activities. This paper studies the different immunological activities of Astragalus polysaccharides at the level of oligosaccharides, laying a foundation for further elucidating the structure and function of Astragalus polysaccharides, enriching the theory of polysaccharide receptors, and providing new ideas for the development of Astragalus polysaccharides.