The DyZn films on the sintered NdFeB magnet surface were prepared through DC magnetron sputtering. The magnetic properties, temperature stability and microstructure of the magnets before and after the thermal diffusion treatment were compared. Under the circumstances of keeping the remanence invariable, the magnet coercivity enhanced significantly from 963.68 kA/m to 1544.60 kA/m with an increasing of 63.31% after DyZn thermal diffusion. The magnet temperature stability could be improved by grain boundary diffusion. The temperature coefficient of the remanence kept constant while that of the coercivity reduced from -0.5533% /K to -0.4885% /K in the range of 293K~453K. Dy elements diffusing along the grain boundary phase mainly aggregated between the grain boundary phase and the grain epitaxial layer via SEM and EPMA with EDS observation.The optimization of microstructure and composition of the grain boundary phase and the formed transition layer (Nd,Dy)2Fe14B between them are the main reasons which causing the coercivity to upgrade dramatically.