Fine multiphase structure and LPSO structure are formed in the hydrogen storage alloy Mg88.7Ni6.3Y5 by microalloying with small amounts of Ni and Y elements. The catalyst (Ni-TiO2)@C is torn as a carbon layer encapsulating on the surface of the alloy particles by ball milling to form Mg88.7Ni6.3Y5+1 wt.% (Ni-TiO2)@C hydrogen storage composites. The Ni and TiO2 in the catalyst accelerate the dissociation of hydrogen molecules. The carbon carrier prevents the agglomeration of nanocatalysts Ni and TiO2. The alloy exhibited exceptional hydrogen ab/desorption kinetics. It can reach 80% hydrogen absorption saturation content within 1 min. The initial hydrogen desorption temperature has been reduced to 200 °C, and the dehydrogenation content is 4.26 wt.% at 250 °C. The adsorption energies of hydrogen atoms at different sites are calculated by Density Functional Theory (DFT). Synergistic catalytic effects were observed in LPSO and (Ni-TiO2)@C.