The invention discloses a preparation method of a nitrogen-doped carbon nanohorn, and belongs to the field of carbon nanomaterials prepared by a direct current arc method. The method comprises the steps that a graphite rod is taken as a negative pole, a graphite rod with holes is taken as a positive pole, a mixture of a certain proportion of nitrogen source and graphite powder is added into the holes, the negative pole and the positive pole are placed vertically, after an electric-arc furnace is vacuumed, buffer gas is introduced and an electric arc is started, and after the reaction is finished, the deposit on the inner wall of a reaction chamber is collected as the nitrogen-doped carbon nanohorn; the prepared carbon nanohorn has high purity, the diameter of each nanohorn is 2-5 nanometers, and the multiple nanohorns are aggregated into a spheroidal aggregate with a diameter of 80-100 nanometers; the method adopts the direct current arc method to prepare the nitrogen-doped carbon nanohorn, and has the advantages of safety, reliability, low cost, simple operation process and the like.