In this paper, based on the method of the RDK method (Repeatedly Direct Kinematics) [1], an optimal algorithm is proposed to apply on implementing weightlifting motion for a robot with multiple joints. According to the proposed algorithm, the optimal motion was generated to minimize load on joints during the lifting motion and subject to basic geometrical and kinematical constraints. To realize the task above, the following two items must be required. First, when the object is lifted up slowly, the robot could stand up as easily as possible and does not tumble down. Second, to reduce the damage to the robot, the load applied on each joint should be as small as possible. Some simulations are presented to evaluate the effect of the algorithm for the weightlifting motion. Next, the robust stability of the system is analyzed to illuminate the influences on the robot from some external factors.