A real-time control system is designed for a tendon-driven five-fingered dexterous hand for on-orbit service. In order to satisfy the special requirements for synchronism and real-timeness of multi-finger operation for tendon-driven hand, a modular software architecture based on RTX (real time extension) shared memory is proposed, which can integrate man-machine interface, virtual display, tele-operation and data transmission. This software architecture has virtues of good scalability, clear structure and high transmission efficiency. The decoupling matrixes from joint-space to tendon-space are presented to solve the problem of tendon-driven coupling, and they are used for the real-time coordinated motion control of multiple fingers to ensure the fingers simultaneously reach the desired positions and decrease the negative effects of tendon-driven delay. Finally, the proposed control system is proven to be stable and reliable by the experiments of multi-finger dexterous grasp and tele-operation.