The invention provides a preparation method of nickel oxide powder, and relates to a preparation method of nickel oxide powder in the fields of battery material, catalyst, magnetic material, electronic material, ceramic and the like. The preparation method is characterized by atomizing nickel salt solution, and thermally decomposing the atomized nickel salt solution under high temperate to obtain the nickel oxide powder. The preparation method comprises the steps of: taking the nickel salt solution as a raw material, atomizing the nickel salt solution under high temperate, thermally decomposing the atomized raw material to generate NiO under controllable atmosphere, and absorbing the generated tail gas to generate regenerated acid. The method can further continuously realize the preparation process from the solution to the NiO, the granularity of the NiO powder obtained by the method is controlled within the range from 0.2 to 20 micrometers, the granularity of the powder is even in distribution, and the performance of the powder is good. The preparation method is energy-saving, environment-friendly, low in preparation cost, and good in economic benefit and social benefit.