The invention relates to a phosphorus-and-slag-free normal temperature coating agent. The phosphorus-and-slag-free normal temperature coating agent is suitable for the metal surface treatment of a plurality of metal materials, such as cold-rolled plates, hot-rolled plates, cast iron, galvanized plates, electrolytic plates, aluminum and aluminum alloys. The phosphorus-and-slag-free normal temperature coating agent is mainly composed of hexafluorozirconic acid, hydrofluoric acid, magnesium nitrate, hydrogen peroxide and water. The coating agent comprises a component A, a component B and a component C, wherein the component A comprises hexafluorozirconic acid, hydrofluoric acid and water; the component B comprises magnesium nitrate, hydrogen peroxide and water; and the component C comprises hexafluorozirconic acid, magnesium nitrate and water. A preparation method of the coating agent comprises the following steps: mixing the component A with the component B according to a certain ratio, fully stirring, and adding water to a constant volume; and adding the component C according to a certain proportion as a supplement to realize adjustment when the concentration of the above treatment liquid decreases. The phosphorus-and-slag-free normal temperature coating agent has the characteristics of strong adhesion capability, strong anticorrosion performance, simple operation method, and no need of the surface adjustment treatment or passivation enclosing, so the process flow is shortened, the coating agent can be repeatedly used for a long term, and the coating agent has a lower cost than traditional phosphatization liquids. Additionally, the environmentally-friendly coating agent contains no nitrites, phosphates, chromium ions or other toxic heavy metal ions or harmful volatile substances, so sewage can be directly discharged without sewage treatment.