The full-actuated parallel manipulator can realize the actuation redundancy of manipulator by increasing one or more constraint branch chain or joint. In order to analyze the optimization of the constrained branch chain and joint to the dynamics performance of the redundantly actuated parallel manipulator, a deep analysis and comparison of dynamics characteristics between redundantly actuated parallel manipulator 6P-US+UPU and non-redundantly actuated parallel manipulator 6P-US were conducted, and the optimization mechanism of constrained branch chain on the dynamics performance of redundantly actuated parallel manipulator was discussed. Based on the principle of virtual work, the dynamics models of non-redundant manipulator 6P-US and redundant manipulator 6P-US+UPU were established respectively. Then according to different influence factors on the dynamics, dynamics performance indexes of redundantly actuated parallel manipulator with clear physical meanings were proposed. The influences of constrain branch chain with and without mass on the different dynamics performance indexes of the manipulator were analyzed subsequently. Prototypes of the two manipulators with specified inertial and geometric parameters were given and numerical comparisons of dynamics performance was carried out finally. The results showed that the branch constraint improved the dynamic performance of the mechanism, while the quality of the branch would reduce the performance.