The invention belongs to the technical field of lithium batteries and provides a simple, convenient and efficient boron oxide coated high-nickel ternary positive electrode material and a preparation method thereof. In a preparation process, liquid pentaborane is added; and the liquid pentaborane is easy to directly and fully mix with a material, the problem that a solvent needs to be treated in wet coating is not required to be considered; the pentaborane can be quickly hydrolyzed to release heat when meeting water on the surface of the material, so that an oxide coating layer can be formed inan extremely short time; long-term sintering is not needed, and therefore, production efficiency is improved; the surface temperature of the material can be increased to meet a coating requirement when the boron oxide coating layer is formed, and therefore, a user does not to worry about insecure coating caused by insufficient temperature; and in addition, the boiling point of the pentaborane isonly 60 DEG C, the pentaborane which does not participate in a reaction is in a gaseous state when the reaction is finished, and therefore, the pentaborane is very easy to separate and recover from the material, and reaction byproduct hydrogen also has a recovery value.