NOVELTY - Preparing 17-alpha-estradiol involves: generating 16,17-O-(alkoxy methylene) epiestriol (A1) from mother liquid of estriol and orthoester; obtaining 3-(un)substituted estra tetraene (A2) by pyrolysis elimination of the compound (A1), followed by reacting with peroxide to obtain 3-(un)substituted 16-alpha, 17-alpha epoxy estra (A3); reacting the compound (A3) with hydrogen halide or hydrohalide-acid to obtain 3-(un)substituted 16-beta-halogenated estra-1,3,5(10)-triene-17-alpha-alcohol (A4), followed by dissolving into solvent (s3), adding catalyst, processing the hydrogenation.    USE - For preparing 17-alpha-estradiol (claimed).    ADVANTAGE - The method provides 17-alpha-estradiol with high yield and high purity; utilizes waste liquid, is environment-friendly; reduces the production cost and increases the economic benefit.    DETAILED DESCRIPTION - A method of preparing 17-alpha-estradiol, involves: (1) generating 16,17-O-(alkoxy methylene) epiestriol from the mother liquid of estriol and orthoester optionally with aprotic solvent (s1) in the acid catalysis; (2) obtaining 3-(un)substituted estra tetraene by pyrolysis elimination of 16,17-O-(alkoxy methylene) epiestriol optionally with solvent (s2); (3) making the 3-(un)substituted estra tetraene react with the peroxide in aprotic solvent (s1) to generate 3-(un)substituted 16-alpha, 17-alpha epoxy estra; (4) making the 3-(un)substituted 16-alpha, 17-alpha epoxy estra react with hydrogen halide or hydrohalide-acid to generate 3-(un)substituted 16-beta-halogenated estra-1,3,5(10)-triene-17-alpha-alcohol; (5) dissolving the 3-(un)substituted 16-beta-halogenated estra-1,3,5(10)-triene-17-alpha-alcohol into solvent (s3), adding catalyst, processing the hydrogenation for respectively generating 3-substituted estra-1,3,5(10)-triene-17-alpha-alcohol or 17-alpha-estradiol; and (6) removing the 3-substituent of the 3-substituted estra-1,3,5(10)-triene-17-alpha-alcohol to generate the 17-alpha-estradiol. INDEPENDENT CLAIMS are included for the following:    (1) preparation of 16,17-O-(alkoxy methylene) epiestriol;    (2) preparation of 3-(un)substituted estra tetraene; and    (3) preparation of 3-(un)substituted 16-beta-halogenated estra-1,3,5(10)-triene-17-alpha-alcohol.