Featured by the potential characteristics of high precision and high stiffness, parallel kinematic mechanisms (PKMs) have great application prospects in the field of precision machining. To develop a high-performance parallel equipment, dimension optimization is a key step. Due to the complex structure with multiple kinematic limbs and passive joints, the change of dimensional parameters may simultaneously influence kinematic performance and engineering feasibility, which makes the dimension optimization of PKMs a challenging issue. In this paper, the motion and force transmission and constraint indices are adopted to evaluate the kinematic performance. Further, all types of possible interferences that influence the engineering feasibility are modeled, and corresponding evaluation indices are established. Finally, the kinematic performance and feasibility evaluation indices are considered together to optimize the mechanism. By virtue of an evolutionary algorithm, a set of feasible dimension parameters of the mechanism is obtained. The results lay the foundation for the development of a 5-DoF Fully Parallel Robot.