The design of a ZnSe-based linear polarizer operating in 3-13 μm broad infrared region with multilayer nanograting structures is performed. The multilayer nanograting structure is formed by a dielectric nanograting that is etched into ZnSe substrate, followed by metal/dielectric/metal thin film structure that are evaporated successively on the top and bottom of the ZnSe dielectric nanograting. An optical cavity is formed on both top and bottom of the ZnSe dielectric nanograting. Polarization characteristics of the proposed polarizer on structural parameters are investigated and an optimized multilayer structure is obtained. An extinction ratio (ER) of higher than 74 dB and TM-transmission (TMT) of averagely higher than 84% in the whole 3-13 μm broad waveband are obtained with a 250-nm-period multilayer nanograting. The ZnSe-based multilayer structure shows the possibility of achieving wide-band and high-performance polarization in 3-13 μm infrared region in a fashion of relatively easy-fabrication, in which no ion etching process is needed for the formation of metallic nanogratings.