The invention discloses a method for catalytic synthesis of benzimidazole derivatives and belongs to the field of organic chemical synthesis. In the synthesis reaction, the molar ratio of aromatic aldehyde to o-phenylenediamine is 1: 1, the molar amount of biodegradable acidic ionic liquid catalyst is 3-5% of the use amount of aromatic aldehyde, the reaction time at room temperature is 7-30min, the volume of a reaction solvent, namely, a mixed solution of water and ethanol, is 4-6 times the molar amount of aromatic aldehyde, the reaction pressure is one atmospheric pressure, the suction filtration is performed after the reaction is completed, and obtained filter residue is dried in vacuum to obtain the pure benzimidazole derivatives. Compared with other preparation method, the method disclosed by the invention has the characteristics that the preparation process is simple, raw materials are relatively cheap, better biodegradability is achieved, the loss is low during the recycling process, the entire preparation process is environmental friendly and is simple and convenient to operate, and the industrial large-scale production is facilitated.