The invention relates to rubber and an adhesive for a capsule in a fuel oil storage tank, and a preparation method of the capsule, belongs to the field of design of fuel oil storage tanks, and is applicable to the industries such as the petroleum industry, the aviation industry and the aerospace industry. The capsule in the storage tank is applied to requirements on forming of large-size rubber capsules, the flexibility of a capsule body is ensured, the overall sealing of a tank body can be ensured, and the cost is low. The large-size rubber capsules refer to the capsules of which the length is greater than 1m and the diameter is greater than 500mm; the capsule in the storage tank has excellent fuel oil and hydraulic oil resistance and can be used at the temperature of 150 DEG C for a long time. A preparation process of the rubber capsule in the storage tank is simple and can be widely popularized.