Graphene nanosheet has recently demonstrated catalytic and agglomeration blocking effects toward MgH 2 nanoparticles. Nevertheless, there is a very limited understanding of the relationship between the structural characteristics of graphene nanosheet and the hydrogen sorption properties of MgH 2 nanoparticles. Using first-principles calculations, we investigate the structural, energetic, and electronic properties of MgH 2 clusters supported on pristine and modified graphene with carbon vacancy or heteroatom (B, N, Si, P, S, Fe, Co, Ni, and Al) doping. The results show that the formation ability of vacancy and heteroatom defects in the graphene lattice is enhanced in the order of vacancy, Al, Ni, S, Co, Fe, Si, P, B, and N. Among them, the B- and P-doped graphene nanosheets, especially the B-doped one, exhibit remarkable synergetic effects toward enhancing the catalysis and confinement of MgH 2 hydride. Analysis of electronic structures shows that the direct bonding between MgH 2 clusters and B/P-doped graphene and the electron transfer from MgH 2 clusters into the B/P-doped graphene are most likely to be the underlying reasons for the improved dispersion and enhanced dehydrogenation properties of MgH 2 clusters.