Abstract: Polysaccharides are biological macromolecules and their biological activities depend on their structure and physicochemical properties. Studies have shown that chemical modification of polysaccharides can significantly increase their structural diversity, improve their biological activities, and even add new biological activities. This article reviews systematacially the research progress of chemical modification of polysaccharides in recent years, including frequently-used methods of chemical modification, the influence of various chemical modification on molecular weight of polysaccharides, physical and chemical properties and spatial structure, the biological activity of chemically modified polysaccharides as well as their pharmaceutical and food industrial application prospect and challenges. It is expected to offer a reference for the further research chemically modified polysaccharides and provide an important basis for the future development of food and medicine based on human health.