Marine macroalgae (including brown algae, red algae, and green algae) exhibit several features of an excellent feedstock for biorefinery, such as high yield of biomass, no occupation of arable land, and no requirement of fresh water. In 2021, the production of brown algae in China was 1.9 million tons, which was much higher than other economic algae. It is worth noting that the carbohydrate content of brown algae is as high as 60%, and three sugars, including alginate, fucoidan and laminarin are unique to brown algae. Amongst them, alginate is a linear anionic polysaccharide which consists of 1,4-linked C-5-epimers β-D-mannuronic acid (M) and α-L-guluronic acid (G). The decomposition of alginate is catalyzed by alginate lyases via β-elimination of glycosidic bonds. They produce various oligosaccharides with unsaturated uronic acid at the non-reducing end, or 4,5-unsaturated uronic acid monomers mannuronate (ΔManUA) and guluronate (ΔGulUA). Fucoidans usually consist of a backbone of α-1,3-L-fucopyranose residues or alternating α-1,3-linked and α-1,4-linked L-fucopyranosyls, and side branches containing glucose, galactose, rhamnose, xylose, mannose or glucuronic acid. The fucopyranose residues may be substituted with sulfate. The highly modified structure of fucoidans can significantly affect the cleavage of glycosidic linkages. Therefore, hydrolases that act on a branched chain and sulfatases are required for the primary degradation. Subsequently, L-fucoses are produced by a series of sulfatases and fucosidases belonging to GH29, GH95, GH107, GH141, GH151, or GH168 families. Laminarin, the storage polysaccharide in algae, is composed of a linear backbone of 20-30 residues of β-1,3-linked-D-glucopyranose and a branched chain of β-1,6-linked-D-glucopyranose. The glycosidic bond in its backbone can be broken by endo-β-1,3-laminarinases (EC 3.2.1.6 and EC 3.2.1.39) and exo-β-1,3-glucanases (EC 3.2.1.58). The β-1,6-glucanase (EC 3.2.1.75) releases glucose by breaking the glycosidic bond in the branched chain of laminarin. Algae-derived polysaccharides and their oligosaccharides have shown health beneficial effects, such as immunomodulatory, antitumor, anti-inflammatory, and other activities, which possess great potential as alternative, renewable resources in cosmetics and functional foods. In this review, we mainly focus on the efficient degradation of brown algae, and summarize the mechanisms adopted by these enzymes for catalysis and conformation changes of substrate specific recognition. Furthermore, it will provide insights for the precise customization of oligosaccharides and the construction of industrial biorefinery platform, thereby promoting the efficient conversion of brown algae.