Subwavelength polarization grating poccesses high efficiency and polarization properties, and it is easy to realize polarization, beam splitting, antireflection, high-reflection, phase delay, etc. The polarization diffraction grating with light weight, small size, performance and stability is a fine new optical component and has tremendous prospect. This paper describes latest developments of polarization gratings polarization characteristics and grating diffraction theory. The metal and dielectric subwavelength polarization gratings are analyszed.