The Redundant Servo Motor (RSM) Approach is applied to the dynamic balancing of elastic linkage mechanism. The principle of RSM is that the real-time variable speed of the motor may be redundant to kinematic motion generation of a mechanism and utilized for the purpose of dynamic balancing of the mechanism. The RSM procedure is applied to a four-bar elastic linkage (as an example). Its elastic dynamic optimization model is established and the balancing principle of the approach is illustrated. Five kinds of motion have been carried on the optimization model. The simulation result has shown the effectivity on the balancing of shaking force and shaking moment and also a great promise by comparing it with the approach which adds an extra servomotor in the mechanism.