A designed Mg_88.7Ni_6.3Y₅ hydrogen storage alloy containing 14H type LPSO (long-period stacking ordered) and ternary eutectic structure was prepared by regulating the alloy composition and casting. The hydrogen storage performance of the alloy was improved by adding nano-flower-like TiO₂@C catalyst. The decomposition of the LPSO structure during hydrogenation led to the formation of plenty of nanocrystals which provided abundant interphase boundaries and activation sites. The nanoscale TiO₂@C catalyst was uniformly dispersed on the surface of alloy particles, and the "hydrogen overflow'' effect of TiO₂@C accelerated the dissociation and diffusion of hydrogen on the surface of the alloy particles. As a result, the in-situ endogenous nanocrystals of the LPSO structure decomposition and the externally added flower-like TiO₂@C catalyst uniformly dispersed on the surface of the nanoparticles played a synergistic catalytic role in improving the hydrogen storage performance of the Mg-based alloy. With the addition of the TiO₂@C catalyst, the beginning hydrogen desorption temperature was reduced to 200 ℃. Furthermore, the saturated hydrogen absorption capacity of the sample was 5.32 wt.%, and it reached 4.25 wt.% H₂ in 1 min at 200 ℃ and 30 bar.