NOVELTY - Bromo-elimination two-step synthesis of finasteride, comprises preparing 2-bromo-dihydro finasteride intermediate by adding an acid binding agent and dihydro finasteride into an organic solvent, adding trimethylchlorosilane, adding pyridine hydrobromide or tetrabutylammonium bromide solution, stirring, washing, separating, concentrating, filtering to obtain crude 2-bromo-dihydro finasteride product, drying, purifying, adding dried product in organic solvent, adding alkali, stirring, separating, concentrating, filtrating, and drying the crude product to obtain white powdered solid substance.    USE - The method is useful for bromo-elimination two-step synthesis of finasteride (claimed).    ADVANTAGE - The method solves the problem of cheap raw materials, has moderate reaction condition and simple separation and precipitation processes; and ensures less side reaction and high yield of finasteride. its environment friendly    DETAILED DESCRIPTION - Bromo-elimination two-step synthesis of finasteride, comprises preparing 2-bromo-dihydro finasteride intermediate by: adding an acid binding agent and dihydro finasteride into an organic solvent, slowly adding trimethylchlorosilane as a catalyst under a nitrogen atmosphere, maintaining the temperature of catalyst addition process at 5-10 degrees C, after 2 hours adding pyridine hydrobromide or tetrabutylammonium bromide solution, stirring at 5-50 degrees C for 2-4 hours, washing to remove slightly excess bromine, separating, concentrating, filtering to obtain crude 2-bromo-dihydro finasteride product, drying the crude product at 40-70 degrees C, and purifying the product using aqueous ethanol precipitation method, where the organic solvent is 1,2-dichloroethane, dichloromethane, chloroform, diethyl ether, tetrahydrofuran, 1,4-dioxane, toluene, benzene, xylene, carbon tetrachloride or N,N-dimethylformamide; and the acid binding agent is 1,8-diazabicyclo(5.4.0)undec-7-ene, lithium diisopropylamide, N-butyllithium, triethylamine, tetramethylethylenediamine or pyridine; and (b) synthesizing finasteride by adding the dried product obtained in step (a) into a reaction flask under a nitrogen atmosphere, adding an organic solvent, reducing the temperature to -20 degrees C to 0 degrees C, slowly adding an alkali to the reaction flask, controlling alkali addition rate, maintaining the reaction temperature at -20 degrees C to 10 degrees C, slowly increasing the temperature to room temperature, stirring for 2 hours, neutralizing excess alkali, washing, separating, concentrating, filtrating to obtain a finasteride crude product, drying the crude product at 40-70 degrees C under a reduced pressure to obtain a white powdered solid substance, where the alkali is potassium carbonate, sodium phosphate, sodium acetate, potassium acetate, sodium methoxide, sodium ethoxide, potassium tert-butoxide, 1,8-diazabicyclo(5.4.0)undec-7-ene, triethylamine, tetramethylethylenediamine or pyridine.