By using the composite cycloid with good adjustable geometric feature as the internal gear tooth profile and on the basis of differential geometry and gear conjugate engagement theory,a meshing equation and a conjugate profile equation of composite cycloid planetary driving with small teeth difference are established,and the line of action,the contact ratio,the mesh boundary as well as the non-undercutting condition are all derived.Then,the induced normal curvature and the pressure angle are analyzed,and the influence of tooth profile adjustment coefficient on the pressure angle is discussed.Finally,a three-dimension solid model of the composite cycloid gear pairs is established,and a dynamic simulation is performed to reveal the meshing relationship as well as the transmission efficiency under certain conditions.The results show that the composite cycloid planetary driving with small teeth difference may result in excellent meshing properties such as multi-teeth meshing,small pressure angle,small induced normal curvature and high transmission efficiency.