The application of the invention discloses waterborne transparent fireproof coating for ancient building wood, made from, by weight, 3-15 parts of a carbided catalyst, 2-10 parts of a purging agent, 2-10 parts of a carbonizing substance, 15-30 parts of ammoniacal copper quaternary, 1-2 parts of UV-531 antiaging agent, 2-4 parts of a synergist, and 65-93 parts of water; a preparation method of thewaterborne transparent fireproof coating for ancient building wood comprises the steps of 1) weighing; 2) preparing guanidine phosphate crystal; 3) grinding the guanidine phosphate crystal, and dryingin vacuum to obtain guanidine phosphate powder; 4) adding the carbonizing substance, ammoniacal copper quaternary and antiaging agent to the guanidine phosphate powder, adding water, and stirring fordissolving to obtain the coating. The waterborne transparent fireproof coating for ancient building wood can keep excellent fireproof performance in ancient building wood in a severe environment.