Abstract: Alginate is an acid polysaccharide contained in brown algae, which is composed of β-d-mannose uronic acid and its C5 isoform α-l-guluronic acid. The degraded oligosaccharides have many physiological activities, such as strengthening plant stress resistance, promoting growth, antibacterial activity, anti-tumor activity, anti-inflammatory activity and antioxidant activity. At present, the preparation methods of algin oligosaccharide mainly include chemical degradation, physical degradation and biological degradation. In this paper, the structure of alginate, the degradation methods of alginate and the physiological activities of alginate oligosaccharides are summarized, the biodegradation methods are emphasized, and the application of alginate lyase and its degradation products is prospected.