The invention discloses a biological fermentation extracting method for hyaluronic acid. The method comprises the following steps of: A, taking streptococcus as an original strain, and taking ultraviolet rays and nitrosoguanidine as mutagens; B, inoculating mutagenic strains to an agar culture medium, and culturing slant strains; C, inoculating the slant strains to a triangular flask; D, inoculating the triangular flask strains to a seeding tank according to a proportion to perform spread culture; E, sterilizing and cooling culture solution in a fermentation tank, and inoculating seeds to the fermentation tank to perform fermentation; F, inactivating the fermentation solution with heating; G, adding active carbon into the fermentation solution to filter decarburized bacteria; H, adding CPB aqueous solution into the filtrate with stirring, and standing and settling the solution; I, adding sodium chloride solution of fermentation solution volume into the sediment, and stirring the solution; J, decolorizing dissociation solution by ion exchange; K, concentrating and purifying the decolorized solution by membrane separation; L, adding ethanol into the concentrate, and separating out the sediment; and M, drying the sediment to obtain the hyaluronic acid. The method has the advantages of feasibility, simple and convenient operation, short production period, low cost, high efficiency, energy conservation and environmental protection. The hyaluronic acid can be widely used in the fields of cosmetics, food, medicaments and the like.