In this paper, an Al film was deposited on the surface of sintered NdFeB magnets by electrophoretic deposition(EPD). It was found that different EPD voltages and times have a great influence on the deposition of Al films. It also investigated the effects of different grain boundary diffusion processes on the microstructure and magnetic properties of the magnet. The results show that the best EPD process is 90 V/30 s. At this time, the combination of the film and the magnet is well, and the thickness is even and moderate. When the grain boundary diffusion process is 500 °C / 1h, the magnet obtains the best comprehensive magnetic properties, and its coercivity, remanence and maximum magnetic energy product are 953 kA/m, 1.41 T and 342 kJ/m3, respectively, which is increased by 30.2%. 0.7% and 11.4%. Through microstructure and composition analysis, it is found that after the grain boundary is diffused, a more flat and smooth rare earth-rich phase thin layer is formed between the crystals, which helps to reduce the demagnetizing field and enhance the magnetic isolation effect, and finally leads to the improvement of coercive force.