The invention discloses a conjugate gear pair based on a common rack, wherein each single tooth profile of the common rack is formed by a cosine-based composite curve composed of a straight line segment I, a cosine curve I, a straight line segment II and a cosine curve II in a rectangular coordinate system, and the straight line segment I, the cosine curve I, and the straight line segment II and the cosine curve II sequentially meet first-order continuous requirements. Each single conjugate tooth profile, corresponding to each single tooth profile of the common rack, of an inner gear or an outer gear is obtained through the meshing principle, and therefore the conjugate gear pair is formed. The whole conjugate gear pair is formed by the single tooth profiles, which are evenly distributed around the center of the inner gear or the outer gear according to the number of teeth of the inner gear or the outer gear, of the inner gear or the outer gear. According to the conjugate gear pair based on the common rack, through the adjustment of the symmetric factor of the tooth profiles, the non-symmetrical gear pair can be obtained, and therefore the long side in the two tooth sides is more suitable for transmission, the short side is more suitable for being used as a seal when the tooth profiles are used as a pump, the separation of a transmission function and a sealing function is benefited, the transmission performance and the sealing performance are enhanced, and a design method of the conjugate gear pair based on the common rack builds a mathematical model for the multivariate optimization of gear pairs.