The invention relates to acid-resistant enamel glaze prepared from fly ash as a raw material and a preparation method thereof. The acid-resistant enamel glaze comprises, by mass, 5 to 35% of fly ash,45 to 65% of SiO2, 0 to 3% of Al2O3, 2 to 6% of B2O3, 0 to 2% of MgO, 0 to 4% of CaO, 6 to 16% of Na2O, 0 to 5% of K2O, 0 to 2% of TiO2, 0.5 to 1.5% of Co2O3, 0.5 to 1.5% of NiO and 0 to 1% of additives. The preparation method comprises blending power plant fly ash and additives according to an enamel glaze formula, carrying out melting at a high temperature, carrying out water quenching, adding acertain ratio of clay, bentonite, borax, a surface modifier and water into the melt, carrying out grinding, coating a metal tube with the acid-resistant enamel glaze slurry and carrying out sinteringat a high temperature to obtain an acid-resistant enamel glaze product. The power plant fly ash has high acid-resistant alumina and calcium content and thus the acid-resistant enamel glaze is prepared from raw materials such as quartz sand and is used for producing an air preheater of a power plant. The acid-resistant enamel glaze realizes energy saving and environmental protection of the whole industrial chain and has good economic benefits. The preparation method has simple processes, is easy to operate and has strong practicality.