of which is served as no grain boundary diffusion treatment and is tested its magnetic property comparing sample 1 the other part is treated by method a in table 4 for grain boundary diffusion treatment after washed and surface cleaning comparing sample 2 the sintered magnet with the process of fine powder heat evaporation treatment is machined to be a magnet with 415 mm and 5 mm thickness the 5 mm direction along the direction of thickness is the orientation direction of the magnetic field the magnets are divided into 4 parts one part of which is not treated with the grain boundary diffusion treatment and is tested its magnetic property comparing sample 3 grain boundary diffusion process the other 3 parts of sintered magnet with the process of fine powder heat evaporation treatment are respectively treated by the grain boundary diffusion treatment according to method a b c in table 4 after washed and surface cleaning magnetic property evaluation process the sintered magnet is tested by nim 10000h type nondestructive testing system for bh large rare earth permanent magnet from china jiliang university oxygen content of sintered magnet evaluation process the oxygen content of the sintered magnet is measured by emga 620w type oxygen and nitrogen analyzer from horiba company of japan the magnetic property and oxygen content evaluation of the embodiments and the comparing samples with the processes of fine powder heat evaporation treatment and the grain boundary diffusion.