Seaweeds are the main ocean plants, which can be used to extract hydrocolloids such as alginate, carrageenan and agar, and many types of bioactive seaweed substances such as fucoidan, seaweed iodine, mannitol, vitamins, polyphenol and minerals. Seaweed polysaccharides and their derivatives such as alginate, carrageenan, agar, oligosaccharides, fucoidan and propylene glycol alginate had gelling, thickening, emulsifying, film forming and many other unique properties which could help improve gastrointestinal systems, and act as antioxidants with related excellent health benefits. They were widely used and highly valued in the development and production of marine functional foods, and were the key areas of research and development in marine functional food products. In this paper, the physicochemical properties and biological activities of algal gum represented by hydromoronate, carrageenan and agaricone as well as algal active substances represented by petrolatum polysaccharide and algal oligosaccharide were introduced, which was great value to further promote the application of algal active substances in the field of functional foods.