The invention discloses an oil testing packer rubber sleeve design method. Not only can the sealing requirement be met, but also drilling in the later period is not affected. The geometric shoulder guard criterion is the characteristic of the end face having to be separated from a sleeve by making an arc by taking the length of the rubber sleeve end slope as the radius; the mechanical shoulder guard criterion is that under the differential pressure condition, the frictional force of the outer ring surface of a rubber sleeve can resist the pressure formed by a supporting ring and the sleeve onthe pressure ring surface, and the rubber sleeve sealing part cannot slide; in addition, a rubber sleeve size criterion formula meeting the sealing condition is given. According to the packer rubber sleeve designed through the method, the shoulder protrusion phenomenon is overcome relying on mechanical characteristics of the rubber sleeve, an auxiliary protruding preventing structure is not used,sealing of the rubber sleeve under large differential pressure is met, the hidden dangers and defects of the rubber sleeve using the protruding preventing auxiliary structure are overcome fundamentally, not only can the sealing requirement be met, but also drilling in the later period is not affected.