The invention discloses a vehicle paint film based on a nanometer composite material. The vehicle paint film is prepared from, by weight, 55 to 65 parts of modified acrylic emulsion, 7 to 10 parts ofthe nanometer composite material, 3 to 4 parts of carnauba wax, 2 to 3 parts of a wetting and dispersing agent, 0.8 to 1 part of a defoaming agent, 0.6 to 0.9 part of a thickening agent, and 30 to 40parts of deionized water. The invention also discloses a preparation method of the vehicle paint film. According to the preparation method, water-soluble modified acrylic emulsion is taken as a paintfilm base body, deionized water is taken as a solvent, VOC content is low, and environment protection requirements are satisfied; and in addition, the modified acrylic emulsion is capable of providingthe paint film with excellent water resistance, and salt spray resistance; the nanometer composite material is capable of increasing the hardness and the adhesion force of the paint film greatly; theobtained vehicle paint film possesses water resistance, salt spray resistance, wear resistance, is capable of protecting vehicle paint effectively, is low in VOC content, is capable of reducing environment pollution degree, no organic solvent residue is left, and vehicle paint environment protection requirements are satisfied.