. In order to improve the dynamic response rapidity and positioning precision for pneumatic 6-DOF parallel robot from the structural design aspect, a mathematical model of natural frequency for the parallel robot is developed based on dynamic equation by using vibration theory. The influences of structural parameters on minimal natural frequency are analyzed by simulation and an optimization rule of structural parameters based on minimal natural frequency is proposed. The optimization rule has advantages of simplification and efficiency, which provides a new theoretical gist for optimization of structural parameters as well as for checking the results of the actual natural frequency for pneumatic 6-DOF parallel robot. And this new rule is also valuable for structural optimization design of other similar parallel robot.