The invention relates to the technical field of chemical coatings and in particular relates to water-soluble paint for wagons and a preparation method of the water-soluble paint. The water-soluble paint comprises 30-40 parts of a styrene-acrylic emulsion, 10-30 parts of an epoxy emulsion, 20-40 parts of water, 0.1-1.5 parts of film formation aid, 20-40 parts of a filler, 1-15 parts of a pigment, 0.1-3 parts of an antirust pigment, 0.1-1.0 part of a neutralizer, 0.01-0.5 part of an antifoaming agent, 0.1-2 parts of a dispersant, 0.1-0.6 part of a substrate wetting agent, 0.1-0.5 part of a flashrust inhibitor, 0.2-0.8 part of a leveling agent and 0.1-0.8 part of a thickener. The preparation method comprises steps of emulsion preparation, color paste grinding and material supplementing. Thewater-soluble paint for the rail wagons not only meets anti-corrosion requirements of the rail wagons, but also meets environment-friendly requirements, and has technical effects superior to those ofconventional similar products.