The large field-of-view optical passive athermalization system realized by using ordinary infrared optical materials has a technical problem that the number of lenses is large, and it is difficult to realize the lightweight and miniaturization when this system is applied to the current new high-resolution, large-area-array infrared detectors. To this end, a chalcogenide glass with a low temperature coefficient of refractive index is introduced, and an optical passive athermalization imaging optical system with a working band of 8－12 μm, a field-of-view of 40°×32.5°, an F-number of 1.0, and a 1280×1024 detector are designed. The design results show that in the operating temperature range of -55－70℃, the modulation transfer function (MTF) values at the detector characteristic frequency of 42 1p/mm are all greater than 0.35. The imaging performance of the system is good, which can meet the requirements of practical engineering applications.