The LiBH4+MgH2 system has great potential for hydrogen vehicle applications. In this study, the reported solid-state hydrogenation system made of LiH+1/2MgB(2) has been investigated using ultrahigh field nuclear magnetic resonance spectroscopy. It is found that Mg-Li ion exchange occurs within MgB2 during ball milling to form a compound of (Mg1-xLi2x)B-2, which facilitates the formation of LiBH4 in the subsequent hydriding reaction. This discovery offers a scientific foundation for investigating the detailed mechanisms of solid-state hydrogenation and dehydrogenation of the LiBH4+MgH2 system in the future