Abstract: In order to apply the method of adding DyH_x at grain boundaries to produce high temperature resistance sintered NdFeB magnet on the production line, this work compared the magnetic properties and thermal stability of magnets prepared by melting adding and grain boundaries adding the same amount of 0.5wt.% Dy at a dysprosium-free substrates, and analyzed the uniformity of the DyH_x grain boundaries added magnet.The mechanism of the increase of H_cj and the improvement of thermal stability by adding DyHx to grain boundary was also studied.The results show that when at room temperature of 20 ℃and compared with the melting adding magnet, the grain boundaries adding magnet has a H_cj increased of 0.32 kOe and B_r increased of 0.09 kGs, and the H_irr decreased more than 21%.The uniformity of the grain boundaries adding magnet is the same as the single alloy melting processes magnet when consider the standard deviation of residual magnetic B_r and irreversible magnetic flux loss H_irr.The improvement of coercive force H_cj and thermal stability of the grain boundaries adding magnets is mainly attributed to the increase of the direct utilization rate of Dy elements and the formation of hard magnetic (Nd, Dy)-Fe-B shells.