Chitosan oligosaccharide (COS) is the only cationic, alkaline, water-soluble polysaccharide found in nature, it has superior biological activity.Chitosan oligosaccharide can improve immunity, inhibit the growth of tumor cells, promote mineral absorption, proliferate beneficial bacteria in human body, and prevent high blood sugar, high blood fat and high blood pressure. Scientific research found that COS has good antibacterial and antioxidant properties, and was an ideal preservative for fruits and vegetables. Chitosan oligosaccharide can also be used as food additives to improve the flavor of the food.