[ $Nd_2Fe_{14}B$ ]permanent magnetic powders ($_iH_c$ = 9.2 kOe, $B_r$ = 12.2 kG) were produced by HDDR process. Their coercivity was enhanced to 12.6 kOe through the grain boundary diffusion process with dysprosium hydride ($DyH_x$). $DyH_x$ diffusion process was optimized through rotating diffusion process, resulting in distinct phases rich in Nd and Dy observable by field emission scanning microscopy and transmission electron microscopy. The mechanism of coercivity enhancement that resulted in restrain the coupling effect between $Nd_2Fe_{14}B$ grains is also discussed.