Abstract: Chitosan which belongs to polysaccharides is abundant in nature,and it is the only polysaccharide which has been used much until now.It is mainly derived from crustacean exoskeleton as well as cell walls of fungi and insects.Due to its strong antibacterial activity,film-forming ability and other properties,it can be used as a good antimicrobial agent in food,fruit and vegetable preservative,food additive and clarifying agent.Because of the chelating properties of chitosan and its derivatives,it can be used to avoid serious damage to ecological balance caused by metal ions in industrial wastewater treatment.Due to the biocompatibility and degradability of chitosan,it can also be used as surgical suture in medicine.The application of chitosan in the food area,printing and dyeing wastewater treatment and medicine area was also introduced.