The preparation method of the nanometer zinc oxide powder described in this invention is as follows: dissolve a soluble zinc salt, potassium hydroxide or sodium hydroxide, and potassium borohydride or sodium borohydride in a molar ratio of 1:0.66:(1-3) into a container containing solvent N,N-dimethylformamide, stir it, heat it to a temperature of 100-200°C for 2-48 hours, then cool it to room temperature, wash the product until the pH value is neutral, and finally wash, filter, and dry it with anhydrous ethanol. The zinc oxide yield obtained by using the preparation method of the nanometer zinc oxide powder described in this invention is close to 100%, with a high purity, particle size ranging from several nanometers to tens of nanometers, and the method is simple. It is an excellent process for preparing ultra-fine nanometer zinc oxide products.