Abstract: Geometrical optimizations of (OsH₂)_n(n=1-⁵) clusters are carried out by using density functional calculation with generalized gradient approximation (GGA) in which electronic spin multiplicities are adequately considered.Ground-state structures of clusters are obtained with optimized geometries' total energy and frequency.For each ground state structure,average binding energy,second-order differences of total energies,magnetic moment and density of states are investigated.It shows that (OsH₂)_n(n=1-⁵) clusters tend to form three-dimensional structures.Interaction between H and Os is strong and (OsH₂)₄ is more stable than its neighbors.Only ground-state geometry of (OsH₂)₅ displays anti-ferromagnetic coupling.Magnetic moment is mainly provided by osmium atoms and is dominant from contributions of d orbitals.