The invention discloses preparation methods of a novel cross-linking agent and a cross-linked polybenzimidazole proton exchange membrane, and belongs to the technical field of fuel cell membrane electrode assemblies. The methods comprises the steps that at first, the novel cross-linking agent containing a benzimidazole structure and a dibromomethyl group is prepared, then a polybenzimidazole membrane is soaked in a solution containing the cross-linking agent, and a cross-linked proton exchange membrane material is obtained. The applied cross-linking process is simple and suitable for all polybenzimidazole membranes, and the cross-linked membranes have much greater mechanical properties, oxidation stability and the like than uncross-linked membranes, and the membranes have the excellent phosphate absorption capacity, and is very suitable for being applied in high temperature proton exchange membrane fuel cells.