Chitosan is a potential polysaccharide resource owing to its specific structure and properties. However, since chitosan itself is insoluble in water at neutral PH, the application of chitosan is quite limited. Therefore, chemical modification of chitosan to make it water-soluble materials is of prime importance for making novel biomaterials. This paper mainly expounds on the chemical modification of chitosan, such as N-acetylated chitosan, hydroxyacylated chitosan, sulfated chitosan, and so on. This paper can serve as reference for further development of chitosan.