The South China Sea contains abundant ocean thermal energy. This paper simulates an OTEC system based on Uehara cycle and considers the actual situation in the South China Sea. The extra middle steam extraction segment is examined to check its influences on the circulating thermal efficiency, the consumption of cold and hot seawater and the circulating exergy efficiency. The results show that in the Uehara cycle Ocean Thermal Energy Conversion System under the working condition of this paper, for the circulating thermal efficiency and the circulating exergy efficiency, there is the best intermediate steam extraction capacity. Different pressures have different optimum values. Concurrently, the circulating exergy efficiency is much greater than thermal efficiency. With the increase of intermediate steam extraction, the consumption of cold and hot seawater both decreased and there is a certain upper limit for steam extraction. The cost of equipment foundation increases with the increase of additional intermediate steam extraction rate, and is mainly concentrated in the heat exchanger. With other conditions unchanged, increasing the working fluid flow can effectively reduce Levelized Cost of Energy (LCOE). When building an ocean thermoelectric power plant, the appropriate intermediate extraction pressure and extraction rate shall be selected according to the specific working conditions.