Based on the rigorous coupled wave analysis method, the diffraction characteristics of bionic moth-eye antireflective cylindrical microstructure is researched at long wave infrared wavelengths. By theoretical analysis and simulation, the effects of the moth-eye microstructure parameters, such as period, depth, filling factor, profile shape in actual manufacturing process on their reflectivity, are discussed. A structure parameters combination is optimized to obtain low reflection. The sub-wavelength period microstructure on germanium substrate is fabricated by binary exposure and reactive ion etching technology. The surface topography is analyzed by thermal field emission scanning electron microscopy, the infrared imaging spectrometer is applied to contrast the germanium wafer with double sides polishing, single-sided and double-sided moth-eye microstructures. The measurement results illustrate that the reflection efficiency of the double-sided microstructures is less than 8% at 8~12 μm wavelength, which achieves the design requirements.