The invention relates to a capsule for a power transformer. The capsule is arranged in the power transformer, and a floating ball is also arranged in the power transformer. The capsule is characterized by comprising a capsule body, a lip structure and an elastic keel, wherein the lip structure is arranged along the extending direction of the capsule body and is located at the outer contour of themaximum section position in the horizontal direction of the inflated capsule body. The capsule lip structure of the V-shaped structure is adopted, and no lowest point position exists on the lip structure, so that the fracture problem of the lip structure cannot be generated, and the capsule damage problem caused by the metal burrs on the inner wall of an oil conservator is effectively avoided. Theadopted elastic keel is arranged on the capsule body, so that the contact part of a capsule lower-layer adhesive tape and the floating ball is smooth, is easy to unfold and does not generate the wrinkles. The floating ball is wrapped, so that the lateral force bending or breaking the connecting rod is avoided, and the phenomenon of false oil level is eradicated. The keel is installed on the outerwall of the capsule lower-layer adhesive tape, and the capsule body is not damaged even if the keel is damaged.