NOVELTY - Extracting diosgenin, comprises (i) taking Dioscorea zingiberensis, cleaning, crushing to obtain paste, adding water, separating the starch and cellulose, adding Rhodotorula glutinis, and fermenting, (ii) fermenting mother liquor, layering, and separating into liquid part and aqueous precipitate, (iii) separating the liquid part of the mother liquor, adding concentrated sulfuric acid, carrying out catalytic hydrolysis, filtering, washing to obtain hydrolyzate, filtering, fermenting, and (iv) drying the hydrolyzate after Soxhlet extraction, crystallizing, and drying.    USE - The method is useful for extracting diosgenin.    ADVANTAGE - The method has simple operation process, and short processing time; consumes less amount of acid; reduces waste water COD; can easily process waste water; can effectively reduce the cost; and reduces the pollution.    DETAILED DESCRIPTION - Extracting diosgenin, comprises (i) taking Dioscorea zingiberensis, cleaning, crushing to obtain paste, adding little amount of water into paste, using a physical method to separate the starch and cellulose, adding Rhodotorula glutinis (0.2-1.2%) into the solid content, and fermenting at 32-40 degrees C for 12-48 hours, (ii) fermenting mother liquor, layering, separating the above liquid part, using the bottom aqueous precipitate fraction for next step, and using the upper supernatant containing Rhodotorula glutinis for the next fermentation process, (iii) separating the liquid part of the mother liquor after fermentation, adding ferric salt or ferrous salts (1.5-4%) into the bottom precipitate, and slowly adding concentrated sulfuric acid or hydrochloric acid into the suspension, where the concentration of the acid is 0.2-1 N, pressure is 0.2-0.3 MPa, carrying out catalytic hydrolysis for 2-3 hours, filtering, and washing to obtain hydrolyzate, filtering the waste filtrate using calcined lime to neutralize, continuing the fermentation process until the chemical oxygen demand (COD) reaches the discharge standard and then recycling, and (iv) drying the hydrolyzate after Soxhlet extraction with solvent gasoline or petroleum ether, then crystallizing, and drying to obtain the diosgenin, extracting the residual cellulose, which is directly used as fuel or other raw material.