The invention discloses a water-based paint for an iron casting through a lost foam casting die. The paint comprises refractory aggregate, binders, a suspending agent, additives and a dispersing agent, wherein the refractory aggregate comprises high aluminum powder, zircon powder and pyrophyllite; the binders comprise silica sol or white emulsion, polyvinyl acetate emulsion, bentonite and sodium hexametaphosphate; the suspending agent comprises sodium carboxymethylcellulose; the additives comprise Tween, octanol, sodium carbonate, cryolite and iron oxide powder; and the dispersing agent is water. According to the paint, suitable ingredients are chosen, the content is adjusted, a suitable mixing process is adopted, and therefore performances such as normal temperature and high-temperature strength, suitable high-temperature permeability and good leveling property, suspension property and painting performance of a coating can be satisfied completely. The paint is suitable for gray iron castings with different trademarks and enables the expendable casting die to be stripped with the iron casting easily, particularly for stripping in flakiness of a sintered coating during cleaning, and the possibilities for diverse defect generation on the surface of the iron casting are reduced; and simultaneously, pollution of coating components to the environment is reduced greatly due to the selection of phosphate assistant.