The invention discloses a method for preparing a high-voltage cathode material lithium-nickel-manganese-oxygen battery. The method comprises a plurality of steps of: dismantling an electric core, immersing the electric core, filtering and separating, preparing acidic filtrate, preparing coprecipiate, and preparing a lithium-nickel-manganese-oxygen battery. The method has the advantages that: 1, comprehensive recycling of Mn, Ni, Li, Al and Cu in waste and old LiMnO batteries, lithium nickel batteries and lithium nickel-manganese batteries is realized, Mn or Ni and Li elements are not needed to be separated, and the new good-performance high-voltage cathode material lithium-nickel-manganese-oxygen battery is synthesized directly; 2, the process is simple, the method is suitable for mass processing, the cost is low, the obtained battery has an impressive market prospect, and the additional value is high; and 3, the recycling rate of manganese and nickel metal in the battery is over 96 percent, and the recycling rate of lithium carbonate is 78 percent.