The invention discloses a preparation method of 3, 4, 5-trifluoro 
bromobenzene. The method comprises the following steps: (1) dispersing 2, 3, 4-trifluoro 
aniline in a 
solvent, dropwise adding 
bromine to carry out a bromination reaction, thus obtaining 2, 3, 4-trifluoro-6-bromaniline through aftertreatment after the reaction is completed; (2) dissolving 
sodium nitrite in 
sulfuric acid, dropwise adding the 2, 3, 4-trifluoro-6-bromaniline obtained in the step (1) while stirring to carry out a diazotization reaction, thus obtaining a diazonium salt intermediate; and (3) under the action of 
hypophosphorous acid and a 
copper catalyst, carrying out a desamination reaction on the diazonium salt intermediate obtained in the step (2), thus obtaining the 3, 4, 5-trifluoro 
bromobenzene through aftertreatment after the reaction is completed. The preparation method has the advantages that the 2, 3, 4-trifluoro 
aniline is adopted as a starting material; the bromination reaction is realized with 
high selectivity; by-products are reduced; the purity and the yield of the brominated product are increased; the final yield and purity of the 3, 4, 5-trifluoro 
bromobenzene are high.