The work aims to improve the stacking efficiency and motion trajectory smoothness of the package handling robot and reduce the vibration caused by the suddenly changed acceleration in the robot motion. With respect to the trajectory characteristics of package palletizing robot, on the premise that the maximum motion velocity of robot was constant, a fifth order S curve optimization method was put forward with the time and impact as optimization indexes. The variable parameters were introduced into the optimized impact force, and the acceleration time of the robot was greatly shortened when the minimal impact was ensured. The simulation results showed that the acceleration and deceleration time of the robot was obviously shortened and the acceleration curve was smoother after fifth order S curve optimization. The optimization method significantly reduces the vibration of the robot due to the sudden change of speed, and effectively improves the working efficiency of the packaging palletizing robot.