In this paper, based on the first-principles method the physical parameters such as lattice constants and bulk moduli of water molecules clathrate and methane hydrate with s-III type are studied. Both the two cage structures can be stable in the pressure range of 0-2.6GPa, and the volume decreases approximately linearly with the increasing pressure. The volume of methane hydrate with the s-III type expands due to the interactions between CH4 molecules, but the increase of volume is smaller and uniform with an average increase magnitude of about 3.97%. Finally, it is found that the methane hydrate with s-III type is an insulator and not conductive according to the calculated band structure and electronic density of states of methane hydrate with s-III type.
