This paper proposes a squat jumping motion control scheme for 4-link robots. The 4-link robot models a human body by 4 links and 3 actuators. Therefore, this system is undreactuated and has variable physical constraints during jumping motion, which makes difficult to control this system. In this work, we design trajectories of the center of gravity to achieve squat jumping motion. Then, we apply input-output linearization and output zeroing control to the system for the designed trajectory. We finally demonstrate the effectiveness of the present approach via simulations.