The invention is environmental-friendly waterborne nanometer fireproof flame-retardant coating and the preparation method, which belong to the fireproof flame-retardant coating manufacturing industry. The flame-retardant coating is obtained through the compounding of two types of flame-retardant agents, waterborne resin, ammonium polyphosphate, melamine, carbon-forming agent, nanometer pigment and filler, micrometer pigment and filler and other auxiliary agent; the flame-retardant coating contains no organic agent and halogen flame retardant, low VOC content, good fireproof property, good physical and chemical properties; the composition of the flame-retardant coating is as follows: the content of waterborne resin is 10-90%; the content of phyllo-silicate nanometer flame retardant which contains phosphor, nitrogen organic intercalation is 1-50%; the content of nanometer magnesium hydroxide flame retardant wrapped by polymer is 1-50%; the content of ammonium polyphosphate is 1-30%; the content of melamine is 1-20%; the content of carbon-forming agent is 1-30%; the content of nanometer pigment and filler is 0.1 to 30%; the content of micrometer filler is 0.1 to 60%; the content of dispersant is 0.1 to 10%; the content of stabilizer is 0.1 to 10%; the content of water is 0.1 to 50%; the content of micrometer pigment is proper; firstly, waterborne resin, nanometer flame retardant, ammonium polyphosphate, melamine, carbon-forming agent, nanometer pigment and fillers, dispersant and stabilizer are put into a planet stirring reactor for stirring and even dispersion; micrometer pigment and filler, water, dispersant and stabilizer are added to the discharged mixture and then put into a high-speed dispersion machine for even dispersion so that the product is obtained.