A method for preparation of Timosaponin BII, which uses Chinese traditional medicine Rhizoma Anemarrhenae or fresh rhizoma or fibrous root of Anemarrhena asphodeloides Bge. as raw material, and comprises isolation of Timosaponin BII by one or more processes selected from solvent extraction, resin adsorption, polyamide chromatography, reversed phase column chromatography, Sephadex LH-20 column chromatography, etc, combining with conventional drying method such as reduced pressure drying, freeze drying, spray drying, and so on. Timosaponin BII obtained by the present method is of over 90% purity, and the method is simple, practicable and suitable for industrial production.