The scarce inventory of cathode materials with reasonable diffusion of Mg ions is the main obstacle in the development of rechargeable magnesium batteries. In this regard, vanadium pentoxide (V₂O₅) has been reported to be a candidate cathode material for Mg batteries. In this study, via first-principles calculations, we showed that the Mg-ion diffusion energy barrier in α-V₂O₅ could be substantially decreased through hydrogenation. It is found that the Mg-ion migration energy barrier in H_xV₂O₅ is gradually decreased with an increase in H concentration. When the H concentration x reaches 2, the migration barrier is decreased to 0.56 eV from that in α-V₂O₅ without hydrogenation (1.28 eV). This indicates that the Mg diffusion kinetics can be substantially improved through hydrogenation, and the resultant energy barrier makes Mg diffusion acceptable even at room temperature. The mechanism of the H-enhanced Mg-diffusion has also been studied, and it has been found that H atoms not only can expand the Mg-diffusion pathway, but also have a screening effect on the interactions between Mg ions and the α-V₂O₅ lattice.