Synthetic method of m-dichlorobenzene

The invention discloses a synthetic method of m-dichlorobenzene which is obtained by transposition in the presence of a catalyst by taking o-dichlorobenzene and/or p-dichlorobenzene as raw materials. The catalyst is a composite catalyst comprising a solid phase catalyst and a gas phase catalyst, wherein the solid phase catalyst is aluminum trichloride or halide of transition metal, and the gas phase catalyst is anhydrous hydrogen chloride or other anhydrous halogen acids. The raw materials have no limitation of water, have arbitrary ortho-para proportion and react under normal pressure; the solid catalyst has long service life, and the gas catalyst can be recycled after gas-liquid separation and has high conversion ratio; and the synthetic method can be used for large-scale industrial production. The process realizes the automatic control easily and has energy saving, safety, environment protection and low cost.