In order to study the influence of the design of magnetic field generating device on the effect of magnetorheological polishing, three magnetic field generating devices based on electromagnet are designed, which are circular array magnetic field, fan-shaped magnetic field and annular magnetic field. Three-dimensional static magnetic field finite element simulation was carried out respectively, and the magnetic field intensity cloud maps, directional cloud maps and magnetic field intensity curves at 5 mm height of different magnetic field generating devices were compared and analyzed. In order to ensure the stability of magnetic field and magnetorheological fluid during processing, different cooling methods were designed for three magnetic field structures to compare and optimize. The annular magnetic field generator was manufactured and integrated into the self-made magnetorheological polishing platform. Anodized aluminum alloy samples were used for polishing experiments. It was founded that a high magnetic field area was formed at the gap of the pole head of the circular array magnet field. As the height increased, the magnetic field intensity decreased rapidly. At the height of 5 mm from the pole head, the magnetic field intensity decreased from 300 mT to about 145 mT, and the magnetic field intensity in the polished area was small. The magnetic field intensity at the height of 5 mm fan-shaped magnetic field was parabolic distribution, with the maximum up to 330 mT. The magnetic field direction was single, and the effective polishing area was relatively small. At the height of 5 mm annular magnetic field, the maximum magnetic field intensity can reach 240 mT. The workpiece was in the high magnetic field area during the whole movement process, and the polishing efficiency was high. The magnetic field intensity and direction of the annular magnetic field generator meet the polishing requirements, and the effective polishing area is large, the surface quality is significantly improved after polishing, and the polishing effect is better.