Polysaccharides have various biological activities, such as antioxidant, anti-tumor, antiviral, anti-aging, anti-inflammatory, anti-radiation, hypoglycemic and lipid lowering, immune regulation, etc. Although many polysaccharides have been proved to have various biological activities, in the research process, it has been found that more polysaccharides in nature do not have biological activities or have low activities, and some polysaccharides have poor activities due to lack of certain groups. While others are due to polysaccharide with too large molecular weight, because its molecular weight is too large to smoothly enter cells and thus cannot exert its activity. For the former, we need to adopt molecular grafting modification. This kind of modification method is mainly chemical modification method, which increases the functional groups and molecular weight of various polysaccharides to improve their biological activity. For the latter, we need to adopt molecular degradation modification, which includes biodegradation, physical degradation, chemical degradation and other means to improve the solubility of polysaccharide in water phase by reducing its molecular weight, thus improving its activity. This article mainly introduces polysaccharide structure modification methods that have been widely used in recent years.