The invention relates to a preparation method of a single-crystal Li(NiCoMn)O2 ternary cathode material, and belongs to the technical field of a manufacturing process for chemical electrode materials. The preparation method comprises the following steps: firstly, nickel salt, cobalt salt and manganese salt are dissolved in a deionized water and ethylene glycol mixed solution, the mixture is uniformly stirred, a surfactant is added, the mixed solution is clarified, a precipitant is added, the mixture is uniformly stirred and poured into a reactor, the reactor is arranged in a drying oven for a reaction, and then an obtained precursor and lithium salt are mixed, presintered and calcined to obtain a target product. The preparation method is simple and convenient to operate, the controllability of preparation parameters is high, the prepared ternary cathode material is a single-crystal material, particle sizes are concentrated at the submicron dimension, a fast conveying channel with the short path is provided for lithium ions, and contact of the material with an electrolyte is increased. The ternary cathode material has high specific capacity, high rate capability and high cycling stability, and meets the requirements of electronic products with high volume energy density.