The polarization-dependent absorption of the rectangular-block perfect absorber metamaterials in mid-infrared regime was investigated theoretically and numerically. The rectangular-shaped nanostructure absorber consisting of metal-dielectric-metal layers has dual-band resonant absorption spectrum at infrared wavelength of 2.0—5.0 μm and its absorptivity is more than 80%. The simulation results indicate that the dual-band resonance spectra of the materials are attributed to the third order resonance mode and the fundamental mode of the perpendicular polarized incident electronic field. A rectangle array optical absorber was developed and its optical properties were measured. The test results show that equivalent permeability of the absorber in two polarized configurations is satisfied the Lorentz model and the imaginary parts of the permeability agree well with the resonance absorption wavelengths, which indicates that the polarization absorption of the materials is depended on the magnetic resonance induced by the incident wave. These results point out that the dual-band resonant absorption mechanism of the nanostructure absorber is conductive to design of biosensors and photoelectric detectors in special wavelengths.