An approach was proposed for the optimal dynamic design of a 4-DOF palletizing robot with closed-chain. On the basis of rigid body dynamic model, a dynamic optimization objective was proposed to minimize the maximum driven torque based on target trajectory and determined motion law. Based on this, a multi objective planning problem under certain constraining condition was constructed and then through shortest distance ideal point method converted to single-objective optimization problem. An example revealed that the robot’s dynamic performance was great improved by optimizing the robot’s scale parameter. The decreasing range of upper and lower arm’s joint torque peak were 9.782% and 8.207% respectively, which show that the optimal dynamic design method is reasonable and effective.