The plenoptic camera can refocus after imaging, and obtain the position and direction information of the target at the same time with one exposure. Compared with the active distance measurement method and the traditional passive distance measurement method, the depth measurement method based on the plenoptic camera has the advantages of being difficult to detect and easy to calibrate. The plenoptic camera 3D imaging technology is a computational imaging technology that integrates the front-end optical system and the back-end information processing. The current research works mainly focus on the back-end information processing algorithm et al. There are few reports on the research of the front-end optical system. Therefore, the design of the front-end optical system was researched. Firstly, a calculation model was established for the depth resolution of a plenoptic camera based on multi-eye vision and the influence of optical system performance parameters was analyzed such as focal length and F-number on the object depth resolution. Secondly, the influence of factors was analyzed such as the blocking ratio of the two-mirror optical system and the magnification of the secondary mirror on the system parameters. Finally, a plenoptic camera main objective optical system for sub-kilometer-scale 3D imaging was designed comprehensively considering the design, processing, assembly, and ranging performance. The focal length of the system is 500 mm, the total length of the system is less than 163 mm, the telephoto ratio is less than 1/3, and the working temperature range is -40 -70 ℃. The full field of view MTF in 80 lp/mm is better than 0.3 at different temperatures. If the plenoptic camera uses this objective and a sub-pixel recognition accuracy algorithm of 1/8 pixel, a depth resolution of less than 5 m can be obtained at 0.5 km.