A kind of planar 3-DOF parallel manipulator is taken as the study object and treated as non-dimensional structure.The design space which can reflect the scope in which the geometric parameters change is presented and the closed-form solutions to invers konematics of the manipulator are solved.The theoretical workspace is calculated and the performance atlases of the theoretical workspace are plotted by utilizing the conditions of the existence of inverse kinematics solutions and design space.According to these atlases

the relationship between the link size and the theoretial workspace of the manipulator is obtained.The distribution rule of the theretical workspace performance indices in the design space is concluded and the better dimension scope of the performance index is given.The atlases are an important base of reference for the mechanism design of this parallel manipulator.