The invention relates to a preparation method of nanometer copper oxide, and belongs to the technical field of inorganic nanometer material preparation. The method comprises the following steps that (1) under the condition of using tripolyphosphate as a template additive, copper salt and hydroxide react to produce copper hydroxide precipitates; (2) the copper hydroxide precipitates obtained in the step (1) take hydrothermal reaction to generate black precipitates; (3) the black precipitates obtained in the step (2) are subjected to centrifugal separation; drying is performed; the nanometer copper oxide is obtained. The tripolyphosphate is used as a crystal core for growing the template; the growth direction of the crystal core is controlled; the nanometer oxide copper with the novel appearance is prepared under the alkaline condition through hydrothermal reaction; the method is simple and convenient; the reaction time is short.