In this paper, kinematics and dynamics of a four-dof differential belt and screw driven parallel robots are analyzed by the multi-body systems using a symbolical formula manipulation. Mechanical characteristics of the idle pulleys and slides, which are difficult to consider by the conventional input/output (from the motor to the end effector) analysis, can be included in the generalized mass and viscosity matrices of the robot by our study. The proposed method was installed by Mathematica then applied to derive the kinematics and dynamics of the robot. The derived results suggest that the robot may be able to perform the iso-inertia and low-interference design.