Abstract: In order to improve the success rate of on-orbit servicing missions for noncooperative targets, a coupled relative motion dynamic model is established for two arbitrary points except center points of mass, during rendezvous and docking between a service spacecraft and a tumbling non-cooperative target spacecraft. Starting from the traditional point-mass relative motion model, a coupled dynamic model is founded for the two docking ports considering the coupling effect produced by relative attitude motion of the two spacecraft and absolute attitude motion of the service spacecraft. The type of coupling effect is analyzed: dynamic coupling effect induced by external moment on spacecraft, kinematical coupling effect induced by relative attitude quaternion, relative attitude angular velocity and absolute attitude angular velocity of the service spacecraft. Finally, a sliding mode controller is designed to achieve safe docking between two docking ports without collision. Numerical simulation results demonstrate that the coupling effect on relative translation is so significant during close proximity and rendezvous that it can’t be ignored.