Abstract: In light of parallel machine tool, the freedom equation is used to confirm the reliability of its concept design. The kinematics theory of multi-body system is used to build the kinematics model of parallel machine tool and the model of showing the relationship between its work space and structure size. Subsequently the relative movement constraint equation of parallel machine tool is adopted to derive the relation equation between its cutter movement and drive rods parameters. The above whole train of thought provides a powerful theoretical basis for guiding the design and control of parallel machine tool and eliminating the blindness of design.