In order to solve the problems of the large number of components and complex structure in the mid-long wave infrared dual-band system, the structural characteristics of the annular folded imaging system was analyzed, and the calculation method of the obscuration ratio was explained. An infrared dual-band annular aperture ultrathin imaging system with common path was designed. The focal length is 50 mm, the field of view is 14°, and F number is 1. The system is made up of only one optical element, so it has simple structure and compact optical path. The ratio of total optical length to focal length is 0.48. At the spatial frequency of 20 lp/mm, the modulation transfer function (MTF) of the full field of view is more than 0.45 in medium wave infrared 3-5 μm, and that is more than 0.30 in long wave infrared 8-10 μm. The athermalization of system is realized in the range of -40-80 ℃. According to the tolerance results, this system is machinable. The chalcogenide glasses used for the substrate material can be precision molded to achieve batch processing. The study provides a new idea for the realization of low-cost and miniaturized infrared dual-band system.