The invention provides a preparation method of a core-shell structure nanometer composite material. The preparation method comprises the steps of taking and placing cobalt powder with grain size being500 nanometers in a container loaded with absolute ethyl alcohol, and placing the container in an ultrasonic oscillator for oscillation and dispersion; weighing and placing tetrabutyl titanate in anabsolute ethyl alcohol solution; adding acetic acid into the absolute ethyl alcohol solution; dissolving deionized water in the absolute ethyl alcohol; dropwise adding the prepared absolute ethyl alcohol solution into a mixed liquid of the acetic acid at a speed of each drop per 10-15 seconds, and performing stirring; and placing the product in a drying box for drying after the mixed liquid formsaerosol, and obtaining a shell-core Co@TiO2 material after taking out. A novel sol-gel method is employed, the fabrication process is simpler, the equipment requirement is relatively low, the operation process is simplified, the cost is reduced greatly and is relatively low, and the preparation success rate is higher.