Dynamics characteristics and motion accuracy analysis are carried out for the 4-RRR redundant parallel mechanismunder high speed and load. The coordinate transformation matrix was used to solve the inverse equation of the plane mechanism,the Jacobian matrix was deduced. Basis on the parallel mechanism was decomposed into the moving platform and the one or two link subsystem, the system dynamics model was established by using Lagrange method, and then the whole dynamics model of mechanism was derived.Taking Matalb/Simulink as a tool, the dynamics of the mechanism was simulated as an example.The simulation results show that the 4-RRR planar parallel mechanism of all the driving member during the movement of the desired trajectory change, driving force and torque values vary for all different numerical values, but positively change law of cosine curve are implemented.The research method is fast and effective, which provides a theoretical basis for the follow-up study.