The present invention relates to a layered lithium-rich manganese-nickel-cobalt oxide positive electrode material preparation method, which comprises: uniformly mixing a certain molar ratio of metal salts of lithium, manganese, nickel and cobalt, and a hydroxide, carrying out a solid phase reaction at a room temperature to obtain a nano-scale lithium-manganese-nickel hydroxide and a metal salt mixing precursor, adopting the metal salt in the precursor as a flux, heating at a high temperature, melting, and adopting the melting material as a reaction medium, such that the precursor is subjected to complete contact mixing and diffusion in the flux so as to achieve a rapid reaction purpose, and the layered lithium-rich manganese-nickel-cobalt oxide positive electrode material xLi2MnO3.(1-x)LiMO2 is prepared, wherein M is Mn1-(y+z)NiyCoz, x is 0.1-1.0, y is 0.1-0.5, and z is 0.1-0.5. Compared to the gas protection coprecipitation method, the sol-gel method and other methods commonly used for preparing the layered lithium-rich manganese-nickel-cobalt oxide positive electrode material, the method of the present invention has advantages of easy operation, practical process, good safety, low cost, high material purity, excellent electrochemistry performance, and the like.