Aiming at high water content problem in the development of offshore oil and gas fields, the solutions adopted by the typical oil and gas fields abroad are analyzed. The feasibility and advantages of the subsea separator development plan for gas fields, especially deep water gas field, is proposed. According to the high water content problem of a deep water gas field in Nanhai, the influence of different external transmission mode of production fluid and installation position of subsea separator is studied, in order to find the optimized plan. The design study of subsea separator is proceeded. The factors to be considered in the subsea separator development plan of high water content gas field is summarized. The research on the design of the subsea separator is helpful for our country to master the design technology of the subsea separator and break the foreign monopoly.