Fucoidans derive from marine brown algae and marine invertebrates,and they are complex sulphated polysaccharides. Fucoidans contain a simple structure mainly composed of fucose units and a large number of sulfate groups and they are polyanion heteropolysaccharides.Fucoidans have a wide range of potential health effects and therapeutic effects,including anti-tumor,immune regulation,anti-virus,hypoglycemia,etc.The chemical structure and sulfate group contents of fucoidans have important effects on their functional activities.Different extraction methods affect the structural composition of fucoidans,and chemical modification can further improve their biological activities.Therefore,this paper aims to summarize the extraction and chemical modification methods,hypoglycemic activity and mechanism of fucoidans,and to predict the future prospects of the research direction of extraction,chemical modification,the structure-activity relationship between fucoidans and hypoglycemic activity and other biological activities,so as to provide theoretical reference for the processing and innovative utilization of fucoidans.