Polysaccharides, also known as polysaccharides, are natural macromolecular compounds composed of more than twenty to tens of thousands of monosaccharides, which are widely found in animals, plants, fungi and microorganisms. Natural polysaccharides can be classified into microbial polysaccharides (fungi and bacterial polysaccharides), medium and low plant polysaccharides (algae-based) and higher plant polysaccharides (if gum, starch, cellulose, hemicellulose, etc.), in animals, depending on their source. Chitin, viscous substances, glycogen, chondroitin sulfate and the like. According to the class of constituent monosaccharides, polysaccharides can be classified into three categories: homopolysaccharides, heteropolysaccharides, and glycoconjugates. Sugar can not only be used as an energy substance and structural component, but also a part of polysaccharide can be used as an energy substance and structural component, and a part of polysaccharide can participate in cell metabolism and physiological regulation. In recent years, reports on the biological functions of active polysaccharides mainly include anti-tumor, hypolipidemic, anti-viral, and immune function enhancement of polysaccharides. At present, polysaccharide as a natural active ingredient has many biological activities, and is non-toxic, harmless, residue-free and drug-resistant. It is favored by researchers at home and abroad, and is a research field in medicine, agriculture and food. Hot spot. In this paper, the research progress of natural active polysaccharides in recent years has been systematically reviewed from the aspects of extraction, separation and purification, biological activity, etc., which provides theoretical reference value for the further research and application development of natural active polysaccharides in the future. 
