The generalized gradient approximation of density functional theory is applied to study the hydrogen storage capacity of the alkali metal atom Li, transition metal atoms Ti and Fe decorated C18B2M(M=Li, Ti, Fe) fullerefles. It is found that the metal is bonding to C18B2 stronger than to C20. When the average adsorption energy of C18B2Li-nH2 is low, and the binding of H2 to C18B2Fe is too strong, C18B2Ti-nH2 has the average adsorption energy between 0.45-0.59 eV, which is in the range from 0.2 to 0.6 eV, so it can realize the reflersible adsorption of H2. A maximum number of H2 adsorbed on to C20B2M(M=Li, Ti, Fe) should be 4, 6, and 4, for Li, Ti, and Fe respectively; this agrees well with the 18 electronic rule. C18B2Li adsorbs H2 molecules mainly through the static electronic field formed by Li ions, while C18B2Ti and C18B2Fe adsorb H2 mainly through the Kubas interaction. Therefore, C18B2Ti can not only adsorb more H2 molecules, but also realize the reflersible hydrogen storage.