Abstract: In this study, a large depth-of-field underwater wide-angle lens was designed based on the characteristics of underwater imaging. Depth-of-field extension technology was adopted to ensure clear imaging of underwater targets at a distance of 3500 mm, and objects within the extended depth-of-field range were clearly imaged by the optical system. The lens achieved a full field-of-view of 90° and focal length of 4.92 mm, with the total optical length controlled within 40 mm. It employed five standard spherical lenses, which significantly reduced the processing difficulty and manufacturing costs, which were thus lower than those of traditional seven-lens structures. At a full-field Nyquist frequency of 83 lp/mm, the modulation transfer function (MTF) of the optical system was better than 0.5, and the imaging quality at the central field-of-view was close to the diffraction limit. Tolerance analysis and experimental verification results demonstrated that the design satisfied the requirements for low-cost mass production and assembly, demonstrating strong potential for engineering applications.