The kinematics of a 4-SPS/CU parallel mechanism was analyzed. In order to quantitatively analyze the influence of joint friction acted as non-conservative force on the mechanism dynamics, the calculation of the normal force corresponding to joint friction was important. For simplifying the dynamics model, the driving chain was treated as a rigid body so the driving friction could be seemed as internal force. Based on the “Coulomb + viscous” friction model, the dynamics model with joint friction of up platform, driving chain and driven chain were built respectively by using Newton-Euler formulation, which could obtain the joint constraint forces/torques with giving motion trajectory of the mechanism’s up platform. Subsequently, the driving friction models were established on account of the relationship between the driving chain’s normal forces and joint constraint reactions. The iterative procedure of complicated dynamics equations was formulated for the effective simulation. The research results showed that joint friction forces significantly impacted on the driving forces of the mechanism.