Infrared (IR) antireflection (AR) coatings are indispensable to optical and electrooptical system, especially to the systems such as IR camera. They are very important for the system to improve the energy output and the optical performance. ZnS is usually used to make lenses for IR systems because of its wideband transmission region. But as a substrate, it is very difficult to deposit AR coatings on ZnS in IR region, especially for the durability. The AR coating is for the ranges of 3.5～3.9 μm and 9～12 μm, and the transmittance required of the spectra is more than 90%. Because there are very few materials that have a wideband transparency available for the long wavelength IR region, it is much more difficult to obtain a good coating which has both good transmittance and good durability. Giving attention to both choosing IR coating materials and meeting the spectra requirement, yttrium fluoride (YF3) was adopted as low-index material at last. But the severe stresses of YF3 would result in chapping if there was not a suitable depositing condition. This problem was solved by utilizing improved techniques such as mixed-vaporizing, ion beam assisted deposition and feasible temperature. The durability, stability and transmittance are all advanced.