A method for preparing a R-Fe-B based sintered magnet, the method comprising: 1) preparing a R 1 -Fe-B-M sintered magnet, wherein the R 1 -Fe-B-M sintered magnet comprises: between 26 and 33 wt.% of R 1 being selected from the group consisting of Nd, Pr, Dy, Tb, Ho, Gd, and a combination thereof; between 0 and 5 wt.% of M being selected from the group consisting of Ti, V, Cr, Mn, Co, Ni, Ga, Ca, Cu, Zn, Si, Al, Mg, Zr, Nb, Hf, Ta, W, Mo, and a combination thereof; between 0.5 and 2 wt.% of B; and the rest being Fe; 2) degreasing, acid washing, activating, and washing by deionized water the R 1 -Fe-B-M sintered magnet obtained from step 1); characterized in that the method further comprises: 3) placing the sintered magnet obtained from step 2) in a sealed box comprising a hot spray gun under a circulating Ar protective atmosphere; employing Tb or Dy as a coating material, and coating a layer of the coating material having a thickness of between 10 and 200 μm on each surface of the sintered magnet by hot spraying, wherein the hot spraying is performed by turning on the hot spray gun to heat and melt a metal wire comprising Tb or Dy, and then directing compressed Ar gas towards the metal wire to atomize and spray the melted metal to each surface of the sintered magnet and forming a coating layer on each surface of the sintered magnet; 4) placing the sintered magnet obtained from step 3) in a vacuum sintering furnace, heating the sintered magnet at a temperature of between 750 and 1000 °C for between 2 and 72 hrs; and controlling a vacuum degree of the vacuum sintering furnace at between 10 -2 and 10 -5 Pa or controlling an Ar pressure in the vacuum sintering furnace at between 5 and 20 kPa to allow Tb or Dy to enter an inner part of the sintered magnet via grain boundary diffusion; and 5) aging the sintered magnet obtained from step 4) at a temperature of between 450 and 600 °C for between 1 and 10 hrs to obtain the R-Fe-B based sintered magnet. 1) preparing a R 1 -Fe-B-M sintered magnet, wherein the R 1 -Fe-B-M sintered magnet comprises: between 26 and 33 wt.% of R 1 being selected from the group consisting of Nd, Pr, Dy, Tb, Ho, Gd, and a combination thereof; between 0 and 5 wt.% of M being selected from the group consisting of Ti, V, Cr, Mn, Co, Ni, Ga, Ca, Cu, Zn, Si, Al, Mg, Zr, Nb, Hf, Ta, W, Mo, and a combination thereof; between 0.5 and 2 wt.% of B; and the rest being Fe; 2) degreasing, acid washing, activating, and washing by deionized water the R 1 -Fe-B-M sintered magnet obtained from step 1); characterized in that the method further comprises: 3) placing the sintered magnet obtained from step 2) in a sealed box comprising a hot spray gun under a circulating Ar protective atmosphere; employing Tb or Dy as a coating material, and coating a layer of the coating material having a thickness of between 10 and 200 μm on each surface of the sintered magnet by hot spraying, wherein the hot spraying is performed by turning on the hot spray gun to heat and melt a metal wire comprising Tb or Dy, and then directing compressed Ar gas towards the metal wire to atomize and spray the melted metal to each surface of the sintered magnet and forming a coating layer on each surface of the sintered magnet; 4) placing the sintered magnet obtained from step 3) in a vacuum sintering furnace, heating the sintered magnet at a temperature of between 750 and 1000 °C for between 2 and 72 hrs; and controlling a vacuum degree of the vacuum sintering furnace at between 10 -2 and 10 -5 Pa or controlling an Ar pressure in the vacuum sintering furnace at between 5 and 20 kPa to allow Tb or Dy to enter an inner part of the sintered magnet via grain boundary diffusion; and 5) aging the sintered magnet obtained from step 4) at a temperature of between 450 and 600 °C for between 1 and 10 hrs to obtain the R-Fe-B based sintered magnet.