After investigating the current status of underwater imaging system, the main factors affecting underwater imaging distance and quality were analyzed, namely backscattering.It breaks through the traditional imaging mode of underwater imaging system with multi-detector and multi-field of view.An underwater imaging optical system with large relative aperture and large field of view was designed by using optical design software Zemax.The system uses only one photoelectric detector with a wavelength of 486 nm~656 nm, a relative aperture of 1/1.8, a field of view angle of 1 200, 9 lenses and no aspheric surface, which simplifies the lens processing process and cost.The size of the Airyspot in the central field of view is 3.When Nyquist frequency is 60 lp/mm, the modulation transfer function (MTF) curves of each field of view are higher than 0.7. At the same time, the high distortion caused by the large field of view system was corrected, results show that the distortion is less than 5%, and the image quality is very good.It can be widely used in underwater exploration, marine development, seabed resources exploration, underwater anti-terrorism and other fields.