Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse (1015～1016 W/cm2) and icosahedral hydrogen atomic clusters H13, H55, H147 and H309 has been studied. The expansion process of the clusters during and after laser irradiation has been examined, showing that the expansion of clusters is isotropic. The expansion scale R(t)/R(0) decreases with the increasing cluster size. This conclusion means that if the cluster size becomes larger, the process of expansion and explosion becomes slower. It is revealed that with an increase in the number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. Because of the symmetrical shell structure of the icosahedron, the distribution of the ionic kinetic energy features some pinnacles. It is also found that the calculated maximal kinetic energy Emax of the produced ions from Coulomb explosion of Hn clusters is roughly proportional to the square of the original cluster size. If laser intensity I increases, the maximal kinetic energy Emax of the produced ions also increases. But after I reaches a certain value Is, the maximal kinetic energy Emax of the produced ions no longer increases, i.e., it will be saturated. The reason is that the atoms in the cluster have been fully ionized, so the increase of laser intensity I doesn′t change the ionized state of the atoms in the cluster. It is concluded that with an increase in the cluster size, the kinetic energies of the produced ions and the laser saturation intensity increase too.