To meet the demand of ankle rehabilitation training in degree of freedom (DOF), workspace and stiffness, this paper proposed a three-DOF parallel mechanism with a novel 3RPS/UPS structure. By adding a redundant driving chain with UPS structure under the foundation of the conventional 3RPS mechanism, the proposed structure can meet the demand of DOF and enhance the stiffness simultaneously. Consequently, the shaking and deformation of the operating platform is decreased, and the operation accuracy is improved as well. In this paper, we conducted a systematic analysis on the aspect of inverse kinematics, workspace and stiffness, and then demonstrated the feasibility of the proposed 3RPS/UPS structure to ankle rehabilitation training with the characteristics of heavy-load, microoperation and so on. To verify the applicability in practical operation of the proposed 3RPS/UPS structure, we conducted kinematics control simulation and obtained a high accuracy in dynamic trajectory tracking.