Abstract: An automatic robot system for orthopaedic operation is introduced, and the parallel robot in this system replaces the traditional reduction tools. A simple and precise targeting method based on a geometric model to get the 3-D path that passes the distal hole of the intramedullary nail is presented, for guiding the serial robot to lock the intramedullary nail. Experimental results indicate that the positioning accuracy and stability of this system are very high, and it reduces the operating time dramatically.