The invention discloses a method for preparing nitrogen-doped molybdenum disulfide nanosheets by a one-step method. The method comprises the following steps: (1) weighing a certain amount of ammonium molybdate tetrahydrate, thiourea and urotropine, dispersing the weighed ammonium molybdate tetrahydrate, thiourea and urotropine in a vessel containing deionized water, and carrying out thorough dissolving and dispersing under the action of ultrasonics and magnetic stirring; (2) transferring the solution obtained in the step (1) into a teflon-lined reaction kettle, carrying out heating in an airblast drying oven for a chemical reaction, stopping heating after a period of time of reaction, and naturally cooling the reaction kettle to room temperature; (3) after cooling the reacted solution to room temperature, centrifuging the reacted solution, collecting a synthesized black substance, and carrying out repeated washing with a mixed solution of deionized water and anhydrous ethanol; (4) subjecting powder, obtained after washing in the step (3), to vacuum drying in a vacuum drying oven until the powder is constant in weight, thereby obtaining the nitrogen-doped molybdenum disulfide nanosheets. According to the method, the cheap urotropine is adopted as a nitrogen source, the reaction temperature is low, the operation is simple, the traditional complicated method is broken through, the yield is high, the catalytic activity is good, and the performance is stable.