A new kind of infrared optical system for imaging guidance of image space scanning is described.The scanning system has the advantages of small size and simple structure, wide FOV for searching and narrow FOV for distinguishing.An infrared optical system was designed.The system has an operating waveband of 3.7~4.8 μm, an effective focal length of 80 mm, the total scanning FOV of ±15° and instantaneous FOV of 5°.The MTF is higher than 0.5 at the spatial frequency of 17 lp/mm across the full FOV.The RMS spot diameter is less than 30 μm.The specifications can meet the requirements of the optical systems.