The invention discloses a method for preparing a high-
coercivity neodymium-iron-
boron magnet through 
grain boundary diffusion, and belongs to the field of magnetic materials. Low-melting-point 
metal is one of Ga, Zn and Sn, low-melting-point 
alloy is prepared from R-M, R is one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho and Y, and M is one or more of Cu, Al, Ga, Sn and Ag. The method comprises the process steps that the surface of a 
neodymium-iron-
boron magnet is cleaned firstly, then the 
magnet is subjected to vacuum preheating, and the magnet is placed in a vacuum melting 
metal or 
alloy solution for hot 
dip coating to achieve 
surface coating; finally, the 
neodymium-iron-
boron magnet obtained after hot 
dip coating is subjected to diffusing heat treatment and subsequent annealing treatment, the 
boundary structure and 
grain boundary phase distribution of the magnet are improved, and the needed high-
coercivity neodymium-iron-boron magnet is obtained. The magnet 
surface coating is even and high in binding strength, and uniformity of the 
grain boundary diffusion process and the structure and performance of the magnet are promoted; meanwhile, the thickness of an attached layer on the surface of the magnet can be flexibly controlled by controlling 
dip coating time and taking-out speed, and waste of 
diffusion source 
metal or 
alloy is avoided; the heat dip 
coating process is continuous, fast and suitable for volume 
continuous production.