Abstract: With the development of space robot and rendezvous & docking technologies, on-orbit servicing is expected to play an increasingly important role in spacecraft life-extension, capacity improvement and space debris removal. So far, the spacecrafts already existed in orbit and the space debris are generally non-cooperative, i.e. neither any artificial marks used for the measurement nor grappling fixtures applied to the capture are mounted on the target. Therefore, robotic on-orbit servicing for non-cooperative spacecrafts has been a hotspot of research in recent years. In this paper, firstly, the characteristics of the on-orbit servicing for non-cooperative spacecrafts are analyzed, and the possible applications of this technology are introduced. Secondly, the achievements of the main space powers are reviewed, and the key technologies of non-cooperative on-orbit servicing are summarized. Finally, the research prospects are presented.