A method is given for synthesis of 2,3,4 trifluoronitrobenzene from 2,3 dichloronitrobenzene by fluorination, chlorination, nitration, etc. The suitable technological conditions were investigated for each steps. In order to increase the yield of fluorination which was the key step, some phase transfer catalysts were used and researched. The result showed that the yield of fluorination was increased about 10% more in phase transfer catalysts than in solvents. As compared with the other methods for preparing 2,3,4 trifluoronitrobenzene, this synthesis route has many advantages with respect to low costs, mild conditions, easy operations, etc. It has been proved that this is a new practical synthesis method in technology and economy.