Cycloidal gear reducers are commonly used for speed reduction where machine needs high reducing ratio and/or high torque drive. In the past decades, a great amount of research has been focused on the design of cycloidal gear reducers and many patents were also invented. Nonetheless, not much research has addressed the topological structure of the cycloidal gear reducers. In the first part of this thesis, the topology of the cycloidal gear reducer is analyzed first. Then structural characteristics of such mechanisms are investigated and summarized. Subsequently, a methodology for synthesizing new cycloidal gear reducer is proposed and new mechanisms are enumerated. In the second part of the thesis, the dynamic analysis of the reducer is conducted via Newton’s law and linear elasticity. Finally, the efficiency of reducer is studied when taking the inertia effect into account. The result shows that the cycloidal gear reducer is able to remain high torque when the mechanical energy varies.