External waterproof and antirust coating composition for automobile exhaust system and application method of external waterproof and antirust coating composition

The invention provides an external waterproof and antirust coating composition for an automobile exhaust system. The external waterproof and antirust coating composition comprises a component A and a component B which are prepared and packaged respectively, the component A is used as an anti-rust prime coat and contains 40-60 wt% of polyphosphoric acid aluminum zinc chromium and the balance of water, and the molar ratio of phosphorus to aluminum to zinc to chromium is 100: (30-35): (3-5): (5-8); the component B is used as a hydrophobic surface coating and is microsphere sandy slurry formed by coating hydrophobic expanded perlite wet micro powder of-200 to + 600 meshes with an aluminum polyphosphate-resole composite glue solution according to the weight ratio of 100: (100-200); the aluminum polyphosphate-resole resin composite glue solution is prepared by mixing an aluminum polyphosphate glue solution and a resole resin solution according to a weight ratio of 100: (80-120). After the outer surface of the exhau