The invention discloses a preparation method of 3,4-di(3,4,5-trifluorophenyl)-2,5-diphenylcyclopentyldienone, which comprises the following steps: by using 3,4,5-trifluorobenzaldehyde as an raw material, vitamin B1 (VB1) as a catalyst and water and ethanol as a mixed solvent, carrying out condensation reaction under alkaline conditions to obtain 1,2-di(3,4,5-trifluorophenyl)-2-hydroxyethyl ketone; by using anhydrous cupric sulfate and ammonium nitrate as a co-oxidant, oxidating the 1,2-di(3,4,5-trifluorophenyl)-2-hydroxyethyl-one in glacial acetic acid to obtain 3,4,5-ditrifluorophenylbenzil; and finally, reacting the 3,4,5-ditrifluorophenylbenzil and dibenzyl ketone in hot ethanol under alkaline conditions to synthesize the 3,4-di(3,4,5-trifluorophenyl)-2,5-diphenylcyclopentyldienone. The method has the advantages of cheap and accessible reaction raw materials, simple synthesis steps, short reaction time, mild reaction conditions and controllable reaction process, and is suitable for industrial production.