As people's life level is improved,the healthy is already became to the important thing that has been focused on.As a kind of functional poly saccharide of chitosan and its derivatives,Application development in medical,health food,non-follution farm,organic agriculture and so on becoming more and more important.But because of the high molecular chitosan is not solved in water,so it's hard absorb in the body,thus it affects its function and use range. Oligosaccharides are based on chitosan,by enzymatic degradation ,the molecular weight is less soluble in water .Large amount of experimental evidence,the oligosaccharides have unique physical activity and function.For example,strengthen your body's immunity,inhibition of tumor metastasis,lower serum cholesterol ,blood lipids,lower blood sugar in diabetics,regulation of intestinal microecological balance,strengthen the antibacterial resistance of animals and plants,etc. .So,oligosaccharides are having a wide range of applications in the fields of medical, biological material ,health food,green agriculture,etc.,which has great potential for market demand.