To meet the needs of the current military infrared imaging instrument, we designed a lens for 8~12 μm wave band with uncooled optical passive method. The specific parameter,F is 1, focus is 40 mm, field of view is 16.8°. The design results are achieved within the scope of the -40~65 ℃, as close to the diffraction limitation. The system does not need focus. The athermalization performance is good.