The work aims to study the shape and working mode of magnet pole so as to improve the uniformity and pro-cessing efficiency of fluid magnetic abrasives on flat aluminum alloy plate. First, the finishing mechanism of fluid magnetic abrasives was analyzed, and the upper magnet pole was analyzed and calculated theoretically. On this basis, three design schemes of upper magnet pole were proposed, and the optimal motion mode of magnet pole was described. Then, the simulation of magnetic field was conducted by Maxwell simulation software and the experimental platform based on the best scheme was set up to finish the experiment. From the simulation results, the magnet pole was designed by distributing embedded tegular permanent magnet. At the same time, the two opposing magnet pole rotated simultaneously to concentrate magnetic energy in the processing area. The highest magnetic induction intensity could reached 0.42 T, thus enhancing the driving effect of magnet pole on fluid magnetic abrasives and improving the efficiency. The results of the machining experiment for flat aluminum alloy plate showed that the larger the rotating speed of the magnet pole was, the faster the reduction of the workpiece surface roughness value Ra was, because the surface roughness of flat aluminum alloy plate decreased from 0.8 μm to 0.3 μm, but when the speed of magnet pole reached 606 r/min, the processing effect began to deteriorate. Therefore, a suitable rotation speed should be selected according to the requirement of workpiece surface quality during processing. Using the opposite magnet pole based on fluid magnetic abrasives to finish the surface of flat aluminum alloy plate can improve the uniformity and processing efficiency.