The suspension plasma spraying technology is used to prepare a Dy2O3 coating with complete structure, controllable thickness and high bonding force on the surface of the sintered Nd-Fe-B magnet, and the coercivity of the Nd-Fe-B magnet is improved by the grain boundary diffusion. The method is to prepare Dy2O3 suspension, and prepare Dy2O3 coating on the surface of sintered Nd-Fe-B by using suspension plasma spraying technology. The particle size of the powder is tested by a laser particle size analyzer. The microscopic morphology, structure and phase composition of the Dy2O3 coating is analyzed by the optical microscope, scanning electron microscope (SEM), energy spectrometer (EDS), and X-ray diffractometer (XRD). The coating adhesion is tested by the coating adhesion automatic scratch tester. The magnetic properties of sintered Nd-Fe-B magnets were tested and analyzed by the NIM-2000H automatic magnetic property measuring instrument. The result is that the grain boundary diffusion Dy2O3 at 875 ℃ increases the coercivity of the magnet from 1161.19 kA/m to 1277.74 kA/m, and the remanence decreases by 0.01 T. The coercivity is improved higher and the remanence decreases slightly. SEM and EDS analysis results show that the improvement of grain boundary structure and the formation of (Nd,Dy)2Fe14B epitaxial layer are the main reasons for the increase in coercivity. It is proved that the suspension plasma spraying-grain boundary diffusion technology is a green and efficient technology for preparing high-coercivity sintered Nd-Fe-B magnets that can control the thickness of the coating.