Abstract: Chitooligosaccharides are natural oligosaccharides composed by β-1, 4-linked homopolymer of 2~10 units of glucosamine (GlcN), and usually prepared by chemical, physical or enzymatic hydrolysis of chitosan. Chitooligosaccharides have many important biological activities, such as preventing and treating metabolic related diabetes, hyperlipidemia, anti-tumor, alleviating degenerative diseases such as Alzheimer’s disease, osteoarthritis, and improving immunity. Many researchers have conducted preliminary explorations on the functional characteristics of chitooligosaccharides and obtained a large amount of effective data, so it has broad development prospects. In this paper, the research on the functional characteristics and mechanism of chitooligosaccharides in recent years are reviewed, and the existing problems in the research are analyzed, so as to provide reference for the further research.