Under the requirements of an underwater large field of view zoom optical system, the selection of optical window and its influence on objective lens were discussed, by which the relative distortion and lateral color induced by the plane window were analyzed and corresponding design methods were given. Regarding the special envelope and working distance requirements of the underwater optical system, a three-part zoom system design model and the design method of the corresponding focusing components were provided by introducing aberration stabilizers in the PNNP structure, dynamic aberration correction capability of the optical structure was improved, also, the problems of the cam curve breakpoints were avoided; by setting the focus lens group in the objective parts, close-range imaging through the entire zoom range was guaranteed. A 4 K underwater large field of view zoom optical system was completed using 3840×2160 high-sensitivity CMOS detector, with 0.5 m-inf working distance, 0.48-0.64 μm work waveband, constant F number of up to 2.8 and 5.9°-62° full field of view. The image quality and tolerance characters are validated by an assembled lens and its underwater imaging experiments.