This invention relates to an extraction process of brown algae polysaccharides in a field of pharmaceutical chemistry. This invention particularly discloses a process of extracting brown algae polysaccharides based on a microwave chemistry method and brown algae polysaccharides obtained by said process. The process of the invention comprises: 1) putting pulverized brown algae powder into a microwave reaction chamber, adding acid solution to conduct reaction; optionally concentrating the mixer, and then washing with organic solvent to remove excess acid; conducting grading alcohol precipitation after water extract to obtain mannuronic acid rich fragment (M rich) algin, fucoidan and/or laminaran respectively; and adding an alkali solution to the brown algae residue to conduct alkaline digestion, filtering the residue off, adjusting pH of the filtrate to neutral, conducting alcohol precipitation to obtain guluronic acid rich fragment (G rich) algin precipitates. The present invention has significant advantages like fast processing rate, high yield of polysaccharides, strong controllable polysaccharide degradation, using less organic acid and efficient recovery, small water consumption, low power consumption, etc., the active polysaccharides has high yield and content, better water-soluble, and good biological activities.