The invention relates to a method for preparing nickel oxide nano particles, and discloses a method for synthesizing nickel oxide nano particles by one step. The method is characterized by comprising the following steps: matching 0.5 to 2 mmol of nickel salt, 2 to 4 mL of surfactant and 5 to 10 mL of 1-octadecene solvent, and selecting the nickel salt, the surfactant and the 1-octadecene for later use; mixing the nickel salt, the surfactant and the 1-octadecene, placing the mixture into three flasks, removing air of the system by adopting water-free oxygen-free technology, and stirring the mixture at the temperature under the protection of nitrogen till the solid is fully dissolved; then, heating the mixture to between 280 and 330 DEG C, reacting the mixture for 5 to 60 minutes after the solution is turbid, and cooling a reaction product to the room temperature; and washing the reaction product twice to thrice by mixed solution of normal hexane and ethanol, and then drying the washed product in vacuum to obtain the nickel oxide nano particles. The method has the advantages of simple process, environmental protection and low production cost; and the obtained nano particles are evenly distributed, the particle diameter is controlled between 50 and 200 nanometers, and the nano particles are expected to have important application in the aspects of catalysis, ceramic and serving as a power supply electrode and the like.