Abstract: The dual-band/multi-band imaging technology get more and more attention. As a key part, the dual-band optical systems, especially medium-wave infrared/long-wave infrared (MWIR/LWIR) imaging systems, becomes one of hot issues research subjects. Catadioptric optical system, off-axis three-reflection optical system and all-refractive optical system were designed, three dual-band imaging optical systems and theirs imaging performance were analyzed. The sensor which can response MWIR and LWIR at the same time was adopted. The main technical indicators are as follows: working waveband are 3-5 m(MWIR) and 8-12 m(LWIR), F/#=2, 2=5.74, f'=100 mm, distortion of the whole field of view is less than 2%, MTF is higher than 0.4 at 16.7 lp/mm in the all field of view. The construction features of the three dual-band imaging optical systems were analyzed and researched, the aberration curves and MTF curves of this three optical systems were presented, the advantages and disadvantages of this three optical systems were summarized.