Based on the design of a docking mechanism, this paper thoroughly investigates the space automatic docking of self-reconfiguration modular exploration robot system (RMERS). The method that leads robot to achieve space docking by using two-dimensional PSD is put forward innovatively for the median size robot system. At the same time, in order to enlarge the detecting extension and the precision of PSD and reduce its dependence on lighting signal, the PSD was remade by increasing the optical device over its light-sensitive surface. The emission board and LED light scheduling were designed according to docking arithmetic, and the operating principle of docking process was analyzed based on these. The simulation experiments were carried out and their results are presented.