Ocean Thermal Energy Conversion (OTEC) is one of the emerging industries of ocean energy and an important link in carbon neutrality. Turbine is a key component of ocean thermal energy conversion, which has an important impact on the performance and energy conversion efficiency of the system. This paper fully considers the application characteristics of ocean thermal energy conversion and the state conversion characteristics of ammonia working fluid. Taking the 100 kW radial inflow turbine in the OTEC application system as an example, based on the design, the turbine is optimized for the key parameters of the turbine stator and the influence of different geometric parameters is analyzed. Subsequently, the optimization results are verified by CFD numerical simulation analysis under different conditions. The results show that the number of stator blades has an important influence on the performance of the turbine. Further optimization studies have shown that through optimization, when the number of stator blades is 33, the internal flow field performance is the best, and the working conditions of the inlet and outlet working fluids are in accordance with the design points without obvious shock wave and reverse flow phenomenon, the efficiency is 89.46%, 3.94% higher than the design value.