Abstract: Si based micro-pillar arrays and micro-cone arrays were fabricated using micro processing technology, the reflection performance of the micro structures was studied in the long wave infrared wavelengths (2.5-9 m) reflection performance of different polarized light. Micro-fabrication combined with modeling analysis of silicon based micro-pillar and micro-cone arrays have been performed to study the effects of structural parameters on the reflectivity of infrared light from 2.5-9 m. Simulation results using rigorous coupled wave analysis (RCWA) method is in line with the test results from a Fourier transform infrared spectrometer (FTIR). It is found that the antireflection characteristics can be obtained for both transverse electric(TE) and transverse magnetic(TM) polarizations, and the micro-cone arrays have lower reflectivity than the micro-pillar arrays. Moreover, the optimized micro-cone arrays show a reflectivity of only 2% or lower from 2.5-6.5 m under TM polarization, with wide-spectrum and omnidirectional antireflection characteristics.