Laser resonator for generating radially polarized beams is designed with aid of a special wire grid polarizer which is used
as the rear mirror in CO<sub>2</sub> lasers. A theoretical model for this resonator with polarization selectivity is established, and the
simulation results show that not only radially polarized modes but also azimuthally polarized modes exist in the laser resonator. In order to guarantee pure radial polarization, the purity of radial polarization needs to be improved by suppressing azimuthal polarization. The purity of radial polarization depends on refractive index of the substrate and grating period of the wire grid polarizer. If the substrate of the wire grid polarizer is ZnSe, the purity of radial polarization can arrive at 85%. When the wire grid polarizer has low refractive index and high ratio of laser wavelength to grating period, pure radial polarization can be obtained.