The invention relates to a method for synthesizing a 4-trifluoromethyl-4-olefine-3-steroidal ketone compound, which takes a 4-steroidal bromine compound as a raw material to carry out a trifluoromethylation reaction and removes a by-product of CF3SO2CH=CHNMe2 generated in the reaction by the simple vacuum sublimation operation so as to achieve the aim of purification. The method has simple and convenient operation and high yield, improves a traditional method which only can remove the by-product by a column chromatography method, and is more suitable for the industrialized production.