According to the meshing theory of noncircular gears, the theoretic equations of pitch curve and its conjugated gears of some common close convex pitch curves, such as ellipse, eccentric circle and Pascal curve were presented. The advantage of this method is that it can be accurately calculated by the computer, and the amendment result of some characteristic parameters on gear pairs can be gained, and for different design requirement can be settled. In addition, the transmission capability and design characteristic of noncircular gear pairs were analyzed