The high-vacuum grain boundary diffusion furnace is a special equipment developed for NdFeB production enterprises to adopt the grain boundary diffusion process of heavy rare earth metal elements. Through the method of grain boundary diffusion, the heavy rare earth metal elements can be effectively introduced around the grain boundaries of the magnet, and at the same time, the usage amount of the heavy rare earth metal elements can be reduced. While realizing the improvement of the coercive force of the magnet, the reduction of the remanence is avoided.