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A new four-degree-of-freedom (4-DOF) parallel manipulator that can produce 3-DOF translations and 1-DOF rotation was proposed. It had two identical limbs connected to the moving platform through passive revolute joints, and each limb had two identical branches driven by a pair of base mounted collinear prismatic joints. Due to such a simple and symmtrical kinematic structure, the 4-DOF parallel manipulator had the advantages of simple kinematics, large workspace, high speed, high positioning accuracy and easy processing. These advantages made it an appropriate candidate for high-speed and high-precision sorting, pick-and-place, palletizing and assembling operations. Compared with similar parallel manipulator, it showed a unique advantage in long-distance high-speed operations. Firstly, the configuration of 4PPa-2PaR parallel manipulator was introduced, the simplified mathematical model of the mechanism was established, the number and nature of mobility were verified with screw theory and the modified Grübler-Kutzbach criterion, and the kinematic characteristics was studied. Secondly, the workspace was determined by a numerical method, the influence of each design parameter on the workspace was analyzed, and the workspace shape and geometric constraint condition were discussed by analytic method in detail. Finally, the ratio of workspace to parallel mechanism itself was determined as the objective function, the design constraints, such as boundary constraints, non-interference constraints, singularity avoidance constraints and workspace shape constrains, were established and genetic algorithm was selected to optimize the size parameters. The results showed that the ratio of workspace to parallel mechanism itself and workspace volume after optimization were significantly increased, and the optimization results provided important guidance for the subsequent prototype development.