This paper presents a control law for a vertical jumping and landing motion with 4-link robot. A target system consists of four links and three actuators placed on each joint between the links. This system is fullactuated at the initial state or posture, but as the physical constraint varies in a process of a jumping motion, the system comes to be underactuated. With the control strategy overcoming these difficulties, we propose a control law of a vertical jumping and landing motion the the model, and numerical simulation.