The invention relates to a preparation method of a novel environment-friendly transparent fireproof coating containing ammonium polyphosphate ester. According to a preparation method, epoxy resin is modified by virtue of diethanol amine, phosphoric acid-phosphorus pentoxide-urea, phosphoric acid-urea and polyphosphoric acid-urea are respectively utilized for reacting with the modified epoxy resin to synthesize a novel water-soluble ammonium polyphosphate ester flame retardant, the flame retardant is prepared into a solution, the solution is blended with melamine-formaldehyde-urea copolymer resin, and the high-performance transparent fireproof coating with dual functions of flame retardance and transparence is obtained by adjusting the proportion of matrix resin and the fire retardant; and the simulation of a big panel combustion experiment shows that the highest fire resistance time of the selected formula can reach 60 minutes and far exceeds the first-level fireproof standard of the transparent fireproof coating. The system of the novel environment-friendly transparent fireproof coating does not contain halogen and organic solvents.