Abstract: Aiming at the problems of Fe grade in tailings of rough low intensity magnetic separation with annular magnetic separator higher than that of the on-site drum magnetic separator in dressing plant of Dagushan，the modification measures by adding an always-on magnet exciting coil to the annular magnetic separation and installing magnetic yoke rings to all the magnetic exciting coils have conducted. The key parameters of the improved annular magnetic separator were investigated and the beneficiation effects of the annular magnetic separator before and after improvement were contrasted. The result showed that under the same parameters and testing conditions，the improved annular magnetic separation not only guarantees the quality of concentrate，but also the percentage of Fe grade reduces 2.2，and the percentage of Fe recovery increased 2.95，the ideal modification effect was achieved.

Key words: Annular magnetic separator, Magnetic system, Always-on magnet exciting coil, Magnetic yoke ring