Abstract: The enlargement of FOV and the relative aperture is the key measure to improve the performance of underwater photographic objective under weak illumination. The characteristics and design methods of WFOV and large relative aperture underwater photography objective under weak illumination are introduced. An underwater photographic objective under weak illumination, whose relative aperture was 1/1.4, underwater FOV was 66° and focal length was 11.8mm, was designed based on the reverse-telephoto structure with 11 optical elements. The imaging quality of this lens was evaluated. The results show that it has an excellent imaging quality, at spatial frequency of 42lp/mm, its MTF value is greater than 0.5 for 0.7ω, and it meets all the specifications and requirements of WFOV and large relative aperture for underwater photographic application.