The invention provides a composite packaging diaphragm and a preparation method thereof. The preparation method comprises the following steps: firstly, adding nitrile rubber, butyl rubber, ethylene propylene rubber, titanium dioxide and talcum powder into an internal mixer, smelting for 10-15 minutes, further adding N-isopropyl-N'-phenyl p-phenylenediamine, 2-mercapto benzimidazole, 2-thiol benzimidazole, dibutyltin dilaurate, ethyl carbamate, zinc oxide, butyrin, glycerol and triethanolamine, continuously smelting for 15-20 minutes, plastifying for 15-20 minutes at 25-30 DEG C, performing straining extrusion by using a straining extruder, finally, vulcanizing by using a press vulcanizer, and molding, thereby obtaining the composite packaging diaphragm, wherein the vulcanization temperature is 140-160 DEG C, the vulcanization pressure is 5-8MPa, and the vulcanization time is 5-10 minutes. The composite packaging diaphragm provided by the invention is very good in mechanical property, very good in elasticity and toughness, excellent in barrier property and good in waterproof property.