Abstract: In order to meet the demanding external dimensions, working environment, and high image quality requirements of long range oblique photography, the optical system adopted a combination of Mersenne-type telescope and lens compensator operating at 0.486 μm~0.656 μm (EO channel) and 3.7 μm~4.8 μm (IR channel), respectively. A tilted beam-splitting plate between the primary and secondary mirrors was adopted to achieve dual band simultaneous imaging and compression of external dimensions. By utilizing the afocal characteristics of the Mersenne-type telescope, a secondary mirror was selected as the image motion compensation mechanism to achieve functions such as aberration correction, back-scanning compensation, and image stabilization. The transfer functions of each field of view in the system are all higher than 0.2 at the Nyquist frequency, and the distortions are all within ±0.5%. The main system and lens compensator can be separately tested and adjusted, and then assembled to reduce the sensitivity of optical fabrication and adjustment.