In this paper, the influence models of different diffraction elements on diffraction efficiency were established, and the diffraction efficiency among single diffraction element, harmonic diffraction element and double diffraction element was compared. The advantages of using double diffraction elements in infrared optical system were analyzed. The average diffraction efficiency of different material combinations was calculated. Based on this, a hybrid infrared dual-band and dual-field optical system suitable for airborne platform was designed. The resolution of the large field of view was 1.5 m@16 km. The long and the short focal length were 960 mm and 480 mm respectively. The zoom function was realized by switching the mirror to ensure the optical axis stability. The simulation results show that the MTF curves are smooth and close to the diffraction limit under the large temperature difference of -40 - +60 ℃. The RMS radius is within the radius of airy spots, and the minimum characteristic size of the binary diffraction surface is 6.9 μm. The design results meet the engineering requirements.