For the demands of light weight and small size, wide field of view (FOV), high resolution, and real-time imaging of the unmanned aerial vehicle (UAV) optical payload, we designed an optical system suitable for the UAV camera using a folding cascade optical structure. The basic components of this system are a front monocentric folding objective and a relay imager. The front monocentric folding objective captures a spherical intermediate image with a wide FOV that is located in the monocentric sphere of the front monocentric folding objective. The relay imager array completes field subdivision, fine correction of residual aberration, and a high resolution relay image on the spherical intermediate image. After optimization, we obtained a folding cascade optical camera system with a full FOV angle of 109.6°, an instantaneous FOV of 7.8", and a tube length of only 107 mm. In the full FOV, the root mean square radii of ray tracing points on the image plane are all less than 1.1 μm. At the spatial frequency of 230 lp/mm, the values of the modulation transfer function are greater than 0.4, and the image quality of the system is close to the diffraction limit. The folding cascade structure UAV airborne camera optical system has a wide FOV, high resolution and compact structure, and can be used in the field of UAV remote sensing. While obtaining a high resolution optical image in a wide FOV, it can also realize the miniaturization and weight reduction of the optical system, which has broad application prospects.