The invention relates to preparation methods of ethylene-propylene-terpolymer-molded sponge rubber and a special-shaped sponge sheath. According to the preparation methods, the roll temperature of an open mill is controlled to be at 70-80 DEG C, and thermal smelting is carried out on ethylene-propylene-terpolymer raw rubber for 5-10 times until rubber materials are all under a uniform transparent state; the roll temperature of the open mill is controlled to be 40-60 DEG C, the thermal smelting is carried out on the smelt ethylene-propylene-terpolymer raw rubber for 10-15 times until the rubber materials are all under the uniform transparent state, and a mixing smelting technology of the open mill is carried out; and sponge rubber strips are longitudinally cut according to the size of a sizing mold by a cutting knife to form crescent sheets, two crescent sheets are respectively put into an upper mold cavity and a lower mold cavity of a special-shaped sizing mold, and the sizing mold is put into a flat-panel vulcanizer for vulcanizing foaming, wherein the vulcanizing temperature is 165-175 DEG C, the vulcanizing time is 3-4 minutes, and the flat-panel pressure is 10-15MPa. For the preparation methods of the ethylene-propylene-terpolymer-molded sponge rubber and the special-shaped sponge sheath, the laboratory investigation is turned into industrial investigation based on the development requirements of automobile industry, the production conditions can be controllable, and the production process is relatively stable.