The invention discloses a high-temperature-resistant substrate-free AB adhesive protective film and a preparation method thereof; the protective film has good high-temperature resistance and can effectively protect intelligent equipment. A PU adhesive layer is introduced to the upper surface of a stripping film, an OCA adhesive layer is introduced to the upper surface of the PU adhesive layer, and a release film is introduced to the upper surface of the OCA adhesive layer; the PU adhesive layer is a polyurethane resin layer, and the thickness of the PU adhesive layer is 10 [mu]m-20 [mu]m; the OCA adhesive layer is an optical hyperviscous adhesive layer, and the thickness of the OCA adhesive layer is 30 [mu]m-40 [mu]m. The protective film has the advantages of high-temperature resistance, no pollution at high temperature and high humidity, good automatic adsorptivity, excellent bubble removing effect and the like, and a glass lens is protected and has no fogging; and the protection performance of the protective film is improved.