The invention belongs to the technical field of anticorrosive coating, and in particular, relates to a metal substrate long-lasting anticorrosive inter-coat and a preparation method thereof, wherein the inter-coat is composed of a component A and a component B, and the component A is composed of the following raw materials in parts by weight: 50-60 parts of an epoxy-organosilicone resin modified acrylic resin emulsion, 12-18 parts of functionalized modified graphene, 10-20 parts of a filler, 8-15 parts of a cosolvent, 0.1-0.5 part of a defoamer, 0.5-1 part of a leveling agent, 0.3-0.8 part ofa water-based drier, 0.3-0.8 part of a thickener, 0.5-1 part of a wetting agent, and 30-35 parts of deionized water; the component B is composed of the components in parts by weight: 40-50 parts of anisocyanate curing agent, and 10-20 parts of a cosolvent. The inter-coat has the advantages of long-term excellent anticorrosive performance, strong adhesion force of the substrate, high mechanical strength, excellent friction resistance, excellent salt spray resistance, good water resistance, chemical resistance, oil resistance and impact resistance, high construction adaptability and the like.