The invention provides a multifunctional composite coating and a preparation method thereof. The composite coating comprises a metal substrate. Anti-corrosion primer paint is sprayed on the surface ofthe metal substrate. Middle thermal insulation paint is sprayed on the surface of the anti-corrosion primer paint. Heat reflection finish paint is sprayed on the surface of the middle thermal insulation paint. High-pressure airless spraying is adopted, the thickness of the anti-collision primer paint is 120 micrometers to 150 micrometers, the thickness of the middle thermal insulation paint is 40micrometers to 60 micrometers, the thickness of the heat reflection finish paint is 60 micrometers to 80 micrometers, and the construction interval of the anti-corrosion primer paint, the middle thermal insulation paint and the heat reflection finish paint is not shorter than 24 h. The multifunctional composite coating and the preparation method are simple in process, and after the composite coating is formed, the multiple functions of long-acting corrosion prevention, efficient thermal insulation, camouflage painting and the like are achieved.