The adsorption property of hydrogen molecules on YmSi@Al12 (m=13) cluster is investigated using the density functional theory. The results show that yttrium atoms do not suffer from clustering on the Si@Al12 cluster. The 18-electron rule can be used to design these systems, and Si@Al12 cluster coated with three yttrium atoms can adsorb 16 H2 molecules with a gravimetric density of up to 5.0 wt%. The calculated adsorption energy of 0.324-0.527 eV/H2 molecule is suited for reversible hydrogen storage in near-ambient conditions.