The invention relates to a preparation method and application of a rod-like nickel disulfide-molybdenum disulfide nano composite. The preparation method comprises the following steps: dispersing nickel nitrate hexahydrate and sodium thiosulfate pentahydrate in deionized water, adding hexadecyl trimethyl ammonium bromide, stirring, adding ethylenediamine, uniformly stirring, transferring into a high-pressure reaction kettle for reaction, centrifugally separating, cleaning with ethanol and deionized water, drying, calcining in a tubular furnace to obtain nickel disulfide, weighing ammonium tetrathiomolybdate and nickel disulfide, adding ammonium tetrathiomolybdate and nickel disulfide into an N,N-dimethylformamide solution, adding hydrazine hydrate, carrying out ultrasonic treatment, transferring the mixed solution into a high-pressure reaction kettle for reaction, centrifugally separating, cleaning with ethanol and deionized water, drying to obtain a rod-like nickel disulfide-molybdenumdisulfide nano-composite, dispersing the composite into a mixed solution of water, ethanol and perfluorosulfonic acid, dropwise coating on the surface of a clean glassy carbon electrode and naturallyair-drying to form a three-electrode system together with a platinum wire and a saturated calomel electrode, wherein the clean glassy carbon electrode is used as a working electrode.