A method for preparing Ulipristal acetate, comprising reaction steps of: wherein R is a hydroxyl protective group, and is selected from -CH(CH 3)OR 1, or 2-tetrahydropyran, R 1 is selected respectively from C1-C10 alkyl or aryl radical; dotted lines in formula V represents that locations of double bonds are at 5, 9, or 4,9, wherein the method comprises steps of: a) utilizing 3,3-(ethylendioxyl)-19-norpregna-5,9 -diene-3,17-dione of formula II as a raw material and utilizing alcohols as a reacting solvent, wherein 3,3-(ethylendioxy)-17β-cyano-7α-hydroxyl-19-norpregna-5,9 -diene of formula III is selectively obtained by a reaction of the starting material and a cyanation reagent under a weak acidic condition at a temperature between -10°C to room temperature; b) obtaining the compound of formula IV by the reaction of the compound of formula III and a hydroxy protective group reagent under the acid condition in a solvent; c) hydrolyzing the compound of formula IV under the acid condition after the reaction of the compound of formula IV with a methylation reagent for obtaining 5,9 -diene-3,20-dione of formula V or 4,9 -dienen-3,20-dione or a mixture comprising both; d) catalyzing the reaction of the compound of formula V and ethylene glycol with the p-toluenesulfonic acid and the trimethyl orthoformate or the triethyl orthoformate at the room temperature in dichloromethane for obtaining 3,3-(ethylene-dioxy)-17α-hydroxy-19-norpregna-5,9 -diene of formula VI; e) epoxidizing the compound of formula VI by hydrogen peroxide for obtaining 3,3,20,20-bis(ethylendioxyl)-17α-hydroxyl-5,10-epoxy-19-norpregna-9 -ene of formula VII; f) providing the addition reaction of the compound of formula VII and a 4-(N,N-diethyl amino) phenylmagnesium bromide Grignard reagent with cuprous chloride for obtaining 3,3,20,20-bis(ethylene-dioxy)-5α-17α-dihydroxy-11β-[4-(N,N-dimethylamino)-phenyl-]-19-norpregna-9 -ene of formula VIII; g) hydrolyzing the compound of formula VIII under an acidic condition for obtaining 17α-hydroxy-11β-[4-(N,N-dimethylamino)-phenyl-]-19-norpregna-9 -diene-3,20-dione of formula IX; and h) acetylating the compound of formula IX with acetic acid, perchloric acid and acetic anhydride at 0∼10°C in the dichloromethane for obtaining Ulipristal acetate of formula I. a) utilizing 3,3-(ethylendioxyl)-19-norpregna-5,9 -diene-3,17-dione of formula II as a raw material and utilizing alcohols as a reacting solvent, wherein 3,3-(ethylendioxy)-17β-cyano-7α-hydroxyl-19-norpregna-5,9 -diene of formula III is selectively obtained by a reaction of the starting material and a cyanation reagent under a weak acidic condition at a temperature between -10°C to room temperature; b) obtaining the compound of formula IV by the reaction of the compound of formula III and a hydroxy protective group reagent under the acid condition in a solvent; c) hydrolyzing the compound of formula IV under the acid condition after the reaction of the compound of formula IV with a methylation reagent for obtaining 5,9 -diene-3,20-dione of formula V or 4,9 -dienen-3,20-dione or a mixture comprising both; d) catalyzing the reaction of the compound of formula V and ethylene glycol with the p-toluenesulfonic acid and the trimethyl orthoformate or the triethyl orthoformate at the room temperature in dichloromethane for obtaining 3,3-(ethylene-dioxy)-17α-hydroxy-19-norpregna-5,9 -diene of formula VI; e) epoxidizing the compound of formula VI by hydrogen peroxide for obtaining 3,3,20,20-bis(ethylendioxyl)-17α-hydroxyl-5,10-epoxy-19-norpregna-9 -ene of formula VII; f) providing the addition reaction of the compound of formula VII and a 4-(N,N-diethyl amino) phenylmagnesium bromide Grignard reagent with cuprous chloride for obtaining 3,3,20,20-bis(ethylene-dioxy)-5α-17α-dihydroxy-11β-[4-(N,N-dimethylamino)-phenyl-]-19-norpregna-9 -ene of formula VIII; g) hydrolyzing the compound of formula VIII under an acidic condition for obtaining 17α-hydroxy-11β-[4-(N,N-dimethylamino)-phenyl-]-19-norpregna-9 -diene-3,20-dione of formula IX; and h) acetylating the compound of formula IX with acetic acid, perchloric acid and acetic anhydride at 0∼10°C in the dichloromethane for obtaining Ulipristal acetate of formula I.