The invention discloses a preparation method of a high-temperature-stability type release film, and belongs to the technical field of preparation of release films. The preparation method comprises the following steps: mixing and heating tetraethoxysilane, absolute ethanol and a hydrochloric acid solution to prepare mixed sol liquid, mixing and standing deionized water, trifluoroacetic acid, isopropanol and the like, collecting the mixed liquid, heating the mixed liquid and the mixed sol liquid, performing evaporation until dryness, collecting the obtained dried crystal balls, ball-milling and sieving, performing mixed grinding and banburying treatment on the crystal balls, polyethylene terephthalate and an antioxidant 1010, collecting the obtained melt material, performing hot-pressing and annealing treatment, and naturally cooling to obtain the stable high-adhesion-rate release film. The release film prepared by the method has high softness, elasticity and release stability, still can maintain high strength and is not liable to release layer residue when being under the high-temperature environment for a long time, and has good use prospect and market promotion value.