The invention relates to a preparation method of rare-earth composite oxides for enhancing heat resistance of silicon rubber, which is characterized by comprising the following steps: preparing a rare-earth salt solution and zinc salt into a mixed solution of which the rare-earth ion concentration is 0.05-2 mol/L, and adding and dissolving a dispersing agent, wherein the rare-earth salts account for 40-80 wt% of the mixed solution, and the dispersing agent accounts for 0.1-3 wt% of the mixed solution; dropwisely adding a 0.1-4 mol/L precipitating agent, and reacting while vigorously stirring until the pH value reaches 7-7.5; and filtering, washing, drying at 70-110 DEG C for 6-24 hours to obtain precursor powder of which the particle size D50 is less than 2 mu m, heating the precursor powder to 900 DEG C at 300 DEG C temperature gradient, and keeping the temperature for 30-180 minutes to obtain the rare-earth composite oxides for enhancing heat resistance of silicon rubber, of which the average particle size is less than 500 nm. The rare-earth composite oxides for enhancing heat resistance of silicon rubber have the advantages of low price, high quality, high heat stability, high chemical stability, no toxicity, no odor and solvent resistance, and can easily implement industrialized production.