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A new type of 3-DOF spatial mechanism composed by closed chain is proposed. The mechanism is constituted by two parallel four-bar linkages which are fixed on a moving platform. The moving platform can not only rotate around its own axis but also can translate along the axis. The four-bar linkage has a crank and does not have the quick-return characteristic. The mechanism has the features of symmetry, high stiffness and large workspace. The details of its kinematics have been described by using analytical method. Firstly, the closed-form solutions of both direct position and inverse position analysis are derived. Secondly, the velocity and acceleration analysis are derived. Thirdly, the boundaries of workspace are given. Lastly, a simulation of workspace in certain conditions will be given.