The present invention relates to a high heat-resistant/oxidation-resistant/flame retardant-non-flammable liquid ceramic coating film for protecting an exterior of an apparatus in an extreme environment. Provided are a method of forming a high heat-resistant coating film including: (a) preparing a liquid ceramic filling agent by mixing a ceramic filler including iron (III) oxide (Fe3O4) powder, a diluent, and an inorganic nanosol; (b) applying the liquid ceramic filling agent to at least one surface of a substrate to form a coating film; and (c) curing the coating film by drying the substrate, and a high heat-resistant coating film prepared thereby.