The invention relates to a preparation method of a core-shell-structure nickel cobalt lithium aluminate and belongs to the technical field of lithium ion battery positive material application. The core-shell-structure material is in a two-layer structure, wherein the inner layer core part is LiNiaCo[1-a-b]AlbO2, a is more than 0.7, b is less than or equal to 0.05 and more than or equal to 0, and a+b is less than 1; the molecular formula of the shell part is LiNicCo[1-c-d]AldO2, c is more 0.5, d is more than 0 and less than 0.5, and c+d is less than 1. In the method, two kinds of aqueous alkali are used as precipitators, so that the materials of the core part and the shell part are consistent in crystal from and compact in structure in the crystallization process, and a solubility gradient method is adopted in the alternating process of the two kinds of aqueous alkali so that the core-shell-structure material is consistent in crystal from and high in crystallization degree, and an obvious core-shell interface does not exist. Compared with a common homogeneous phase material, the core-shell-structure material disclosed by the invention has the advantages that the high capacity is kept, the cycling stability and the heat stability are improved, the air expanding rate is obviously reduced, and the cost performance is higher, so that the core-shell-structure material is more suitable for being used in power batteries.