The invention aims to provide a preparation method of a cathode material lithium nickel cobalt manganese oxide of a lithium battery. Soluble nickel, cobalt and manganese salt are taken as raw materials, and the method is characterized by comprising specific process steps as follows: 1) preparation of a nickel-cobalt-manganese precursor through coprecipitation: soluble nickel, cobalt sulfate and manganese chloride are taken as the raw materials, water is added, a nickel, cobalt and manganese salt mixed aqueous solution is prepared, a sodium hydroxide aqueous solution is added as a precipitant, ammonia water is taken as a complexing agent, coprecipitation is performed under conditions of heating and alkali presence, a filtrate and filer residues are obtained through filtering, the filter residues are cleaned, and the nickel-cobalt-manganese precursor is prepared; 2) preparation of a lithium nickel cobalt manganese oxide product through mixing: the prepared nickel-cobalt-manganese precursor is dried, ground and stirred and mixed sufficiently with lithium salt, the mixture is loaded in a bowl, calcined, sintered, broken screened, dried and packaged, and the cathode material lithium nickel cobalt manganese oxide is obtained; the calcining and sintering time and the sintering temperature are controlled. Full-automatic controlled production is adopted in the production process, the production operation is convenient, reaction conditions are mild, and the prepared ternary cathode material lithium nickel cobalt manganese oxide has excellent performance.