A RPR-type multi-redundantly actuated parallel mechanism 2RPU+2UPR+RPR with freedom of two-rotation-one-translation was proposed. It can be used to design a variety of robots used in heavy loads and precision occasions. Motion and constraint screws about the mechanism were analyzed based on the screw theory, and with that the number and properties of degrees of freedom were analyzed. Kinematic model of the mechanism was developed and validated by simulation results. Transfer screw system of the mechanism was derived, and motion/force transfer index of the mechanism were established, including local and global performance index. In addition, the distribution characteristics of the performance index was analyzed. Dimension of the mechanism was optimized based on the quality workspace and quality transfer performance, and the optimized dimension was obtained, as well as the transmission performance map at the optimized dimension. What’s more, the influence of key dimension parameters on the mechanism transfer performance was analyzed. To verify the results of the dimension optimization, singular properties at the optimized dimension were analyzed based on Jacobian matrix and transmission performance maps. The research result would provide a reference for the theoretical research and application of this multi-redundantly actuated parallel mechanism.