Sintered neodymium-iron-boron magnet and preparation method thereof

The invention relates to a sintered neodymium-iron-boron magnet and a method for preparing the sintered neodymium-iron-boron magnet. The method comprises the following steps that S1, a sintered neodymium-iron-boron magnet base material is prepared; s2, a diffusion source containing RE is attached to the surface of the sintered neodymium-iron-boron magnet base material, and then grain boundary diffusion treatment and tempering treatment are carried out; rE is Dy and/or Tb; wherein the grain boundary diffusion treatment comprises initial diffusion heat treatment and N stages of diffusion process sections, N is greater than or equal to 1, and each stage of diffusion process section sequentially comprises high-temperature diffusion heat treatment and low-temperature diffusion heat treatment; the conditions of the low-temperature diffusion heat treatment are as follows: the temperature is 850-950 DEG C, and the time is 6-12 hours; the temperature of the high-temperature diffusion heat treatment is lower than that