To reduce the polarization sensitivity of antireflection gratings, a particular rectangular structure was analyzed by genexating equivalent medium theory(EMT) to two-dimensional subwavelength structure. An approximate equivalent coefficient for two-dimensional subwavelength was obtained with the related expressions of grating structure. A two-dimensional subwavelength antireflection grating designed for 10. 6 μm was fabricated on a Si substrate by using binary optical processing. The results show that this grating st ructure was similar to a single antireflection film at 10. 6 μm.