The mathematic model of joint friction in mechanical system was put forward, in which the action forces in joint were converted into ideal constraint force and friction moment. The friction was dealt as exterior non-inertia force, and the dynamics equation including nonlinear friction of planar 5-bar parallel mechanism using the method of reduced model was presented. A sliding mode controller was designed for compensating the influence of nonlinear friction and time variable parameters. The stability analysis using Lyapunov’s direct method shows that the controller is asymptotically stable. The results of experiment demonstrate the effectiveness of the proposed model and controller.