The invention discloses a transparent intumescent fire-retardant coating and a preparation method thereof. The transparent intumescent fire-retardant coating comprises, by mass, 20 to 50 parts of a flame retardant, 15 to 25 parts of a binder, 9 to 15 parts of a foaming agent, 0 to 5 parts of an auxiliary agent, 0 to 15 parts of a filler and 10 to 30 parts of a solvent. The preparation method comprises adding the solvent and the binder into a reactor, adding the flame retardant, the foaming agent, the auxiliary agent and the filler into the reactor along with stirring and carrying out full mixing to obtain the transparent intumescent fire-retardant coating. The transparent intumescent fire-retardant coating has high flame retardant efficiency, can be used in a humid environment for long time, prevents flame retardant precipitation and does not reduce transparency. The preparation method has simple processes, realizes a low production cost and can be easily industrialized.