Most optical instruments for military and aerospace application are expected to perform over a wide temperature range. The variation of the temperature will change the len's curvature, thickness and interval, as well as their refractive index and the refractive index of the surrounding. Because of the large temperature coefficient of the matcerial's refractive index, infrared optical systems often suffer from the performance degradation seriously. For this reason, several active or passive compensation mechanisms have to be appended to thermal imaging systems to compensate the performance degradation with temperature changes. Thermal properties of the refractive lens and diffractive lens are studied, and a method for designing athermal diffractive-refractive hybrid system in infrared region is introduced. An infrared diffractive-refractive hybrid optical system in 8～14 μm with 16°field of view is designed. In this system, two materials of Zinc selenide and Germanium are used, and the image quality of the system achieves diffractive limit at the temperature ranging from -20 ℃ to 60 ℃, with a compact structure and light weight.