Abstract: By using dynamical equations of short distance relative motion with consi deration of the size of space station, the conditions and relative motion trajectories for astronaut departing from large size space station are studied. At the positions on up outside, down outside, downward fore outside or upward back outside, 1) when not bound, the astronaut will drift freely without power, his relative motion mode in orbit plane is ellipse with drifting center; 2) the relative motion mode in orbit plane for powered departure is straight line, steady ellipse or ellipse with drifting center. These results are essentially different from those based on the model of space station as mass point. Depending on departure positions or departure velocities, different extravehicular relative trajectories could be achieved in order to satisfy various requirements.