The invention discloses a synthetic method for 2,4-difluorobiphenyl, and belongs to the technical field of halogenated biphenyl. The method uses 2,4-difluoroaniline and benzene as raw materials, the 2,4-difluoroaniline is diazotized, and the diazotized product and the benzene are subjected to a coupling reaction to obtain the 2,4-difluorobiphenyl; and the method comprises the following steps: adding trifluoroacetic acid, anhydrous magnesium sulfate, a catalyst and the benzene into a reaction kettle, performing cooling under stirring to temperature of 2-6 DEG C, adding isoamyl nitrite, controlling temperature at 6-10 DEG C, adding the 2,4-difluoroaniline dropwise, controlling reaction temperature at 10-25 DEG C in the adding process, after material addition is completed, performing a reaction under stirring for 1-3 h at temperature of 5-12 DEG C, after the reaction is completed, performing suction filtration on the reaction mixture, performing washing, performing drying, and performingreduced-pressure distillation to obtain the 2,4-difluorobiphenyl. The synthetic method disclosed by the invention is simple, and the synthesized 2,4-difluorobiphenyl has a high yield and high purity.