The invention discloses a high-nickel single-crystal ternary cathode material with low surface residual alkali content and a preparation method thereof. The preparation method comprises the followingsteps: weighing lithium hydroxide, an oxide additive and a nickel-cobalt-manganese ternary precursor, and carrying out uniform mixing through a dry high-speed mixing process so as to prepare a mixed material; subjecting the mixed material to first sintering so as to obtain a first sintered material; crushing the first sintered material, and carrying out sieving so as to obtain a first crushed material; weighing the first crushed material, a coating agent and deionized water, and carrying out water washing under stirring so as to prepare a slurry, wherein the coating agent comprises an elementX which is one or more selected from the group consisting of B, Al, Ba, Zr, Mg, Ca, Ti, Si, V, Sc, Nb, Ta and Z; drying the slurry under a vacuum condition through a dynamic rotary drying process so as to obtain a dry material; subjecting the dry material to secondary sintering so as to obtain a secondary sintered material; and crushing the secondary sintered material, and carrying out sieving soas to obtain a product. The high-nickel single-crystal ternary cathode material and the preparation method thereof provided by the invention has the following advantages: alkali reduction by water washing and in-situ coating by a wet process can be synchronously completed; the process is simple; high compaction density is realized; and the content of residual alkali is low.