The invention discloses a nanometer water-based fireproof coating. The nanometer water-based fireproof coating comprises a component A, a component B and a component C, wherein the mass percentages ofthe component A, the component B and the component C sum to 100%. The component A comprises the following raw materials in percentage by mass: 0.1 to 0.2% of cellulose, 0.8 to 1.5% of propylene glycol and 0.1 to 0.2% of inorganic bentonite, 12%-12.5% of ammonium polyphosphate, 10%-12% of melamine, 8%-9% of pentaerythritol, 2%-3% of chlorinated paraffin, 2%-3.5% of nanoscale titanium dioxide, 1%-1.5% of nanoscale silicon dioxide, 4%-5% of talcum powder, 10%-10.5% of wollastonite powder, 8%-8.5% of mica powder, 0.3% of microsphere powder and purified water. The component B comprises 8 to 10% ofan emulsion and 6 to 8% of a silicone acrylic emulsion. The component C comprises 0.1-0.15% of a defoaming agent. According to the invention, the carbon layer strength of the coating after combustionis increased, a compact carbon layer film is formed, flame retardant effect is more outstanding, fire endurance can be increased to 2 h, and cost is saved.