The invention relates to a material for a decorative ring of a vehicle lamp and discloses a polyester alloy composite material for the decorative ring of the vehicle lamp and a preparation method thereof. The prior art has the defects that the prime coat treatment of the decorative ring of the vehicle lamp makes the processing cost increased and the production efficiency reduced, and a prime coat solvent volatilizes to pollute the environment. The polyester alloy composite material is prepared from the following raw materials in part by weight: 48.2 to 93.7 part of polybutylene terephthalate, 5 to 30 parts of polyethylene glycol terephthalate, 1 to 20 parts of inorganic filler, 0.1 to 0.6 part of antioxidant, 0.1 to 0.6 part of nucleating agent and 0.1 to 0.6 part of ester exchange inhibitor. The components are fused and blended at the temperature of between 210 and 280 DEG C so as to prepare the polyester alloy composite material. The invention has the advantages that: a step of spraying the prime coat is avoided, aluminum is directly plated, the production technology is simplified, and the production cost is reduced; and the surface of the material is high in glossiness, high in heat resistance and low in haze, and the phenomenon of lamp fogging is avoided.