In the infrared optical system with a large field-of-view, the optical passive athermalization system based on ordinary infrared optical materials has the technical problems of a large number of lenses, and it is difficult to achieve lightweight and miniaturization. To solve this problem, a combination of chalcogenide glass and common infrared materials is used to achieve passive optical athermalization, and a miniaturized uncooled infrared imaging optical system with a field-of-view of 40°×32.5° is designed. Its operating waveband is 8～12 μm, the F number of the optical system is 1.0, and the operating temperature range is -55℃～+70℃. The design results show that the system has a simple and compact structure and good imaging performance. The modulation transfer function(MTF) value at the spatial frequency of 42 1p/mm is greater than 0.3, which can meet the application requirements of actual projects.