The invention discloses a preparation method of a bronze historical monument corrosion inhibitor with a double-sulfydryl plane structure. The preparation method comprises the following steps: preparing diazonium salt, i.e., dissolving 1.12g of NaSH crystal into 20mL of an absolute ethyl alcohol solution in a 100mL test tube, and cooling the obtained solution to 5 DEG C or below for later use; dropwise adding ethyl alcohol solution of NaSH slowly into a diazonium salt solution obtained in the step S1 while stirring, adjusting the pH value of the reaction liquid to 7-8 by using an NaOH solution after dropwise adding is finished, then continuously stirring and carrying out a reaction for 3h; standing for 30min, so that coarse 2,5-mercapto benzimidazole-fine granular white precipitate is separated out; carrying out suction filtration to obtain a crude product; recrystallizing the coarse 2,5-mercapto benzimidazole in a solution of absolute ethyl alcohol and water to obtain 1.81g of pure white 2,5-mercapto benzimidazole, wherein the ratio of the absolute ethyl alcohol to the water is equal to 1: 1.