Abstract: A scanning imaging optical system of dual infrared spectrum is studied, and combined with the triple imaging technology and 100% cold shield efficiency technology, a common-aperture dual-channel infrared scanning imaging optical system was designed. The system was composed of a common twomirror system, a beamsplitter, a collimation system, a scanning mirror and an imaging system. Light was divided into the mid-wavelength infrared (MWIR,3 m～5 m) waveband and the long-wavelength infrared (LWIR, 10 m～12 m) waveband by the beamsplitter, then they were converged on the two detectors through the collimation system and imaging system, and the MWIR and LWIR optical systems realized common-aperture synchronization imaging. The use of small scanning mirror greatly reduced the scanning mirror-s difficulty of manufacture and test, the difficulty of designing the control mechanism, and reduced the system size and weight. The result shows that the LWIR system transfer function is above 0.4 at 18 lp/mm, and the MWIR transfer function is above 0.78 at 18 lp/mm, which satisfies the needs of practical applications.