The invention provides a highly stable lithium nickel cobalt aluminate positive electrode material and its preparation method. The characteristic chemical formula of the lithium nickel cobalt aluminate material is LinNi1-x-yCoxAlyO2.mLiMaOb, wherein n is not less than 0.95 and not more than 1.15, x is more than 0.00 and less than 0.30, y is not less than 0.01 and not more than 0.10, m is more than 0.00 and less than 0.05, a is more than 0.0 and less than 3.0, b is a valence matching coefficient, and b is (M valence * a +1) / 2. The morphology of the material is a spheroidic secondary particle structure formed by a primary particle, the average particle size of the primary particle is 0.10-2.5mum, and the average particle size of the secondary particle is 3.0-20.0mum. LiMaOb is a composite oxide lithium ion conductor coating and is uniformly distributed on the surface of the primary and secondary particle, so the removal and embedding of lithium ions in the battery charge and discharge process are promoted, and the side reactions of the lithium nickel cobalt aluminate material and an electrolyte can be inhibited. The above lithium ion battery positive electrode material has the advantages of high energy, high safety and long cycle life.