Transmission and negative refractive index (NRI) of metal-dielectric-metal (MDM) metamaterials perforated with different thickness of dielectric layer are studied. It can be found that transmission peaks of rectangular hole are sensitive to the thickness of the dielectric layer. NRI and the bandwidth of NRI are increased with the increasing of the thickness of dielectric layer. NRI of rectangular hole with the thickness of dielectric layer almost follows a linear law when the thickness of dielectric layer in 2–5 μm. A high NRI of metamateriral can be obtained by adjusting the thickness of the dielectric layer of the rectangular hole on MDM metamateriral arrays.