In order to obtain high-quality flat mirror, a serial mode combined polishing technology, consisting of continuous polishing (CP) and ion beam figuring (IBF), is presented. The function of CP technology is to get certain figure accuracy and meet the requirements of the surface roughness of the flat mirror. The final high figure accuracy of the flat mirror is achieved by the IBF technology. We introduce the polishing principles of CP and IBF and then, the polishing experiment and material removal function of IBF are studied. Finally, a F 160 mm flat mirror is polished by a serial mode combined polishing technology. After serial mode com-bined polishing, the surface error and roughness of the flat mirror are 2.06 and 0.42 nm RMS, respectively. The experiment results indicate that the serial mode combined polishing technology is effective for polishing ultra-precise flat mirror.