In order to improve the target detection and recognition ability and enhance the environment adaptability of infrared optical system, thermal and chromatic properties of infrared optical materials in MLIR and LWIR were analyzed, acoording to the requirements of optical power distribution, axial achromatic aberration and athermal aberration in the dual infrared band, properly lens materials were choosed based on the infrared chromatic diagram. And a dual-band infrared athermal optical system was designed. The system based on no cooled staring detector, the wavelength spectrum was 3-5 μm and 8-12 μm, The system consisted of four lenses, the effective focal length was 50 mm, the relative aperture was 1:1.25, the field view was 14° and the total optical focal length was just 67.9 mm. The result shows that between -50-60 ℃ and at the modulation transform function of 17 lp/mm is greater than 0.4 both in MWIR and LWIR, which prove that the system can work correctly at a large temperature range.