A method for preparing an alumina-based solid solution ceramic powder by means of a combustion synthesis water mist method, wherein the raw materials are separately dried, mixed well, loaded into a high-pressure reactor, and the raw materials are ignited under a reaction atmosphere to carry out a high-temperature combustion synthesis reaction; a high-temperature melt is obtained after the reaction is complete, then a high-pressure reactor nozzle is opened after thermal insulation; under the action of a high-pressure gas in the high-pressure reactor, the melt is sprayed at a high speed, and is rapidly cooled by means of a liquid phase to obtain an alumina-based solid solution ceramic powder. The method does not have high particle size requirements for the raw materials, and a micron-scale powder is utilized, thus costs are greatly reduced, the efficiency of processing is high and industrial production may be carried out.