The invention discloses a coating composition directly painted on a rust layer. The coating composition is prepared from the following components in percentage by mass: 30-40 percent of epoxy resin powder, 5-10 percent of dicyandiamide system, 10-20 percent of chlorinated polyethylene powder, 3-10 percent of melamine derivative, 15-26 percent of anti-rust pigment, 20-31 percent of filler, 1-5 percent of aluminum stearate and 5-10 percent of solubilizer. The coating composition has the advantages of no pollution, high adhesion force, high tolerance on a rust layer of a base material and good corrosion resistance, and can be widely applied to painting on the rust layer.