The invention provides a method for preparing nickel-cobalt-manganese composite oxide powder, and relates to a preparation method of a battery cathode material. The preparation method is characterized by comprising the following processes of: atomizing a nickel salt, cobalt salt and manganese salt mixed solution used as a raw material, carrying out thermal decomposition at high temperature in a controllable atmosphere to obtain the nickel-cobalt-manganese composite oxide powder, and absorbing generated tail gases to form regenerated acid. The method can be used for preparing the nickel-cobalt-manganese composite oxide from the solution continuously in one step, and the nickel-cobalt-manganese composite oxide powder prepared by the preparation method has the advantages of controllable particle size in the range of 0.2-20 mu m, uniform particle size distribution, uniform composition and excellent performance. The preparation method has the advantages of energy saving, environmental protection, low production cost and significant economic and social benefits.