The invention relates to heat-resistant filter paper and a preparation method thereof. The heat-resistant filter paper disclosed by the invention is composed by the following raw materials by weight: 52-60 parts of hardwood pulp, 42-52 parts of calcium carbonate powder, 10-18 parts of carboxymethyl cellulose, 12-13 parts of polyester fiber, 3-4 parts of trimethylolpropane, 1-2 parts of hydroxyl silicone oil, 2-3 parts of nanometer bentonite, 1-2 parts of celestite powder, 1-2 parts of sodium persulfate, 1-2 parts of antimonous oxide, 1-2 parts of lauryl dimethyl amine oxide, 2-4 parts of sodium dodecyl sulfate, 2-3 parts of triethylene glycol, 0.6-1 part of gamma-aminopropyl triethoxysilane, 3-4 parts of a wet strength agent, 2-4 parts of rosin, 4-5 parts of aluminum hydroxide powder, 3-4 parts of glycerin, 5-7 parts of absolute ethyl alcohol, 0.1-0.3 part of peroxide tert-butyl acetate, 0.2-0.4 part of dodecyl alkylphenol polyoxyethylene ether and a proper amount of water. By adding a great amount of calcium carbonate powder as a raw material, the heat resistance of the filter paper is greatly improved.