Abstract: A hybrid refractive/diffractive IR thermal imager with light weight and wide temperature range was designed. The working wavelength was 3.7 m～4.8 m; the relative aperture was 1/2; the efficient focal length (EFL) was 120 mm ; the full field of view was 5.18and the system satisfied 100％ cold shield efficiency. The system was designed with three lenses and two kinds of materials-Si, Ge-and an aspheric surface and a diffraction surface to realize operation with light weight and wide temperature range. The imaging quality of the system approaches to the diffraction limit at -60℃～160℃. It is compatible with the staring midwave infrared detector which has a format of 256256 and the pixel pitch of 30 m. The system can recognize the tank from 2.3 km.