A new method for on-line fabrication of micro tool-electrodes is presented in this paper. The method is base on the machining mechanism of electrochemical micromachining. By exchanging the polarities of the tool-electrodes and workpiece repeatedly, micro tool-electrode appropriate for electrochemical micromachining can be obtained through mutual machining. Because the processes are carried out on-line, the position error and clamp error caused by twice-clamp of tool-electrodes can be avoided, and the machining precision can be improved greatly. This method will be very important to electrochemical generating micromachining. Experiments are carried out, and a tool-electrode with the pinpoint of 20μm can be machined stably.