The method for extracting dioscin and diosgenin includes the following steps: pulverizing rhizome of Chinese yam plant by adding water, fermentation by using lipolytic enzyme, separating cellulose and lignin, recovering supernatant, suspension and starch, mixing recovered liquors and filtering residue, boiling and filtering, repeating for several times, filtering residue for stand-by, combining filtrates and concentrating, using ethyl alcohol to make reflux extraction, cooling and filtering, decompressing and concentrating filtrate, adsorbing, evaporating, ethyl alcohol extracting, adding ethyl ether, cooling to room temp. and separating out tetrasaccharide saponin, recovering ethyl alcohol and ethyl ether from supernatant, precipitating out saponin, drying, adding water in starch and filter residue, regulating pH, adding alpha-amylase.