The metal-rubber composite-cycloid gear pair with a small tooth difference has small volume and compact structure. Metal rubber has a strong deformation compensation ability and can help realize high precision transmission. The structure and principle of the composite-cycloid gear pair were introduced, and a three-dimensional model of the gear pair was established to explore the influences of structural parameters of rigid and rigid-flexible gear pairs on their dynamic characteristics. After a rigid flexible mixed model of the metal-rubber gear pair was established in ADAMS, the dynamic simulation of the metal-rubber gear pair with a small tooth difference was carried out. The influences of the changes of elastic modulus, the clearance of the double gear, and the distance between the centers of the two pairs of gears on the angular velocity, the angular acceleration, the meshing force, and the transmission error of the metal-rubber gear pair were analyzed. At the same time, the differences of the angular velocity and the transmission error between the rigid and rigid-flexible composite gear pairs were analyzed. The results show that the vibration fluctuation can be reduced by increasing the distance between the centers of the gear pair with a small tooth difference, and increasing the elastic modulus of metal rubber and the clearance of double gear. The angular velocity and the transmission error of rigid-flexible composite cycloid gears are smaller than those of rigid gears, indicating that the metal rubber plays a role in reducing vibration in the new NN gear pair with a small teeth difference.