The invention discloses a preparation method of a benzimidazole compound. The benzimidazole compound has the following structural general formula (shown in the description), wherein R1 represents aryl and substituted aryl; and R2 represents fluorine, chlorine, methoxy, methyl or acetyl. By virtue of the preparation method, the benzimidazole compound is synthesized from o-nitro benzene halide and amine in the presence of a copper catalyst and an alkali additive for the first time; no additional oxidizing agent and reducing agent are added, and the reduction of nitro, the oxidization of amino and the amination of halogen can be realized by virtue of an oxidation reduction catalysis system, so that the cost is low, and the operation is simple.