The invention discloses a preparation method of an inorganic binder for iron founding and relates to the technical field of casting. The method comprises the specific steps: 1) pre-treating silicon dioxide nanoparticles; 2) modifying the pre-treated silicon dioxide nanoparticles; 3) preparing a tungsten oxide nanosheet; and 4) adding sodium silicate, methylsilicone oil, sodium tripolyphosphate andsec-alkyl sodium sulfinate into distilled water, stirring the mixture till the system is clarified, and then adding the modified silicon dioxide nanoparticles and the tungsten oxide nanosheet to obtain the needed inorganic binder. The inorganic binder is applied to casting production to improve the strength and ventilating property of sand effectively, so that the pig iron casting quality is improved favorably.