The invention relates to a nano-composite coating and a preparation technique thereof, specifically to a preparation process of a high Al content AlTiN nano-composite coating. The AlTiN nano-composite coating is prepared on a metal or hard alloy matrix by adopting an arc ion plating technique. To better adjust and control the contents of Al and Ti elements in the coating, pure metal Al and Ti(with purities of 99.9wt.% and diameters of 80mm) are adopted as targets, and 4 pure Ti targets and 4 pure Al targets are alternately uniformly distributed on the inner wall of a furnace body to improve the coating uniformity. The preparation method comprises the steps of: before coating, leading in Ar gas, turning on the Ti target, carrying out bombard purging on the matrix surface for 10-30min, then depositing a metal Ti transition layer, finally leading in reactant gas N2, and carrying out build-up of luminance on the Ti and Al targets simultaneously to deposit the AlTiN coating. The AlTiN nano-composite coating provided by the invention has simple preparation process, good repeatability and easy industrial production, and the prepared AlTiN coating has the advantages of higher hardness and strength, good high-temperature oxidation resistance and corrosion resistance, compact organization structure and strong binding force between the coating and the matrix.