Abstract: In order to realize the attitude stability of a service spacecraft and a target spacecraft after docking in on-orbit servicing missions, an attitude coordination control approach for the combined spacecraft is proposed based on the estimated coupling torque of a manipulator. Firstly, the dynamic modeling and analysis of the space manipulator and the combined spacecraft are established. Secondly, the attitude of the combined spacecraft is adjusted by the coordinated motion of the space manipulator, which takes advantage of the dynamic coupling between the combined spacecraft and the space manipulator, and the corresponding coordinated planning approach is presented. Furthermore, the attitude of the combined spacecraft is controlled by the space manipulator with assistance of the reaction wheels, since the fuel in traditional spacecrafts is limited and the reaction wheels are prone to be saturated. Next, the coordinated attitude controller is designed based on the estimated coupling torque of the space manipulator. Finally, the proposed coordinated control method is analyzed and compared with the conventional spacecraft attitude control method through simulation. The results show that the proposed method can achieve the attitude stable control of the combined spacecraft through the space manipulator and the reaction wheels, without using expensive jet fuel.