The invention relates to a thermal insulation coating and a preparation method thereof, and the preparation method comprises the following steps: adding hollow granular micro-bubbles made of special materials, hollow glass beads and an opaque polymer on the basis of a water base, a bonding agent base material and a filler, combining active hydroxyl genes thereof with a molecular chain of an emulsion polymer and forming a dense net layer structure in a coating, wherein the coating has the comprehensive thermal insulation function of reflecting, blocking and radiating solar heat and has the significant effects of thermal insulation and energy conservation. The coating has strong adhesion to the surface of a building, the thickness of a coating dry film is only 60 mu m-150 mu m, and the coating is not only thermal-insulating, but also water-proof. The coating has excellent air permeability and long-lasting antibacterial property, as well as the advantages of pollution prevention, self-cleaning, sound isolation, aging resistance, long service life, easy construction and manpower conservation; compared with the traditional thermal insulation material, the coating has excellent performance-price ratio.