With the properties of the Li-Mg-N-H system improved by the doped Ti species, the activation energies of these systems were estimated by an Arrhenius plot, and this elucidated a slightly decreased value with doped TiF 3 . To explore the nature of Ti species in the Li-Mg-N-H system, the crystal structure of Li 2 MgN 2 H 2 with doped Ti was calculated and determined as Li 7 TiMg 4 (N 2 H 2 ) 4 by a first principle approach. As a result, the Li-N and N-H bonds in Li 7 TiMg 4 (N 2 H 2 ) 4 were markedly weakened, which were evaluated by the energies of Li/H vacancy formation. Moreover, the weakened Li-N bonds indicated a considerable improvement in hydrogen absorption of Li 2 MgN 2 H 2 with doped Ti, which was close to the experimental results. Otherwise, the weakened N-H bonds indicated a theoretical possibility that Li 2 MgN 2 H 2 could be destabilized for further hydrogen desorption at an elevated temperature.