Abstract: The dual-band infrared optical system can track the band informantion stretch from mid-wave infrared to long-wave infrared, which can greatly improved the information acquisition. A dual-band infrared optical system based on the compact principle was designed, the optical system can imaging clearly continuous from 4.4-8.8 m/17.8-8.8 m, the F# strictly matched with cold light bar that the cold light bar effect reached 100%. While the system using the passive athermal methods to get rid of temperature compensation problem and finally realized the dual-band of athermalization. The result shows that: the design of the system structure is relatively simple, and can get stable good imaging quality in continuous bands from -40 ℃ to 60 ℃, satisfying the requirements of a standard infrared thermal imager.