The invention discloses entropy-stabille RE2O3-AO2-B2O5 oxide ceramic and a preparation method thereof, and the preparation method comprises the following steps: taking raw material rare earth oxides RE2O3, AO2 (A = Ti, Zr, Hf, Sn, Th and Ce) and B2O5 (B = V, Nb, Ta and P), calcining, cooling, carrying out ball milling, drying, sieving to obtain powder, carrying out spark plasma sintering, and finally carrying out heat preservation, annealing and carbon removal to obtain the compact RE2O3-AO2-B2O5 rare earth oxide ceramic which takes RE2A2O7 and RE3BO7 as matrixes and is of a fluorite type or pyrochlore type structure is obtained. The fluorite type or pyrochlore type rare earth oxide ceramic material which is high in lattice defect concentration, low in heat conductivity, high in hardness, excellent in fracture toughness, high in phase purity and high in density is prepared by regulating and controlling the stoichiometric ratio of different metal elements and through the steps of high-temperature, high-pressure and short-time sintering; and the material can be applied to the fields of thermal barrier coatings, environmental barrier coatings, solid oxide fuel cells, nuclear waste storages and the like.