In this article, we study the stable control of tethered despin of a massive rotating space object in a central gravity field by a small space tug. A control scheme under the passivity-based model predictive control framework is designed to ensure that the constraints of state and input (bounded libration angle, positive tether tension, and bounded thrust) are satisfied. Furthermore, an additional passivity constraint is introduced into the passivity-based model predictive control to guarantee the asymptotic stability of the closed-loop control system. The attainable equilibrium configuration of the tethered system is first analyzed. Then, a framework of the storage energy function is constructed by the potential energy shaping methodology to establish the passivity mapping of the tethered system from input to output. Finally, the strictly asymptotic stability of despinning control of the tethered system under the proposed control law is theoretically proved by the invariance theorem and Lyapunov stability theory. The effectiveness of the proposed control scheme is verified by numerical simulation.