The invention discloses a preparation method of a fluoro aromatic compound, which comprises the following steps: (1) preparing arylamine hydrofluoride from
hydrogen fluoride and arylamine in a ring reactor, and (2) enabling the arylamine hydrofluoride to flow into a diazotization ring reactor, and adding
solid sodium nitrite into the diazotization ring reactor in proportion by a continuous feeder to carry out diazotization reaction; (3) transferring the diazotization product to carry out
solid-liquid separation, and enabling the liquid to flow into a multi-stage
pyrolysis annular reactor; (4) the multi-stage annular
pyrolysis reactor comprises at least three stages of annular
pyrolysis reactors, the pyrolysis temperature is gradually increased according to the inflow direction, and the
temperature difference between the adjacent annular pyrolysis reactors is 3-10 DEG C; and (5) carrying out post-treatment to obtain the fluoro
aromatic hydrocarbon compound. According to the method disclosed by the invention, the byproduct
sodium bifluoride is recovered by
solid-liquid separation of the diazonium liquid, and the tandem ring-shaped reactors can realize full-process
automation, so that the reaction is accurately controlled, reliable, continuous and stable, few organic byproducts are generated, the yield is as high as 92% or above, and the purity is as high as 99.97%.