In recent years, the seawater temperature of some nuclear power plant sites in South China has increased significantly compared with the original design stage. As the final hot sink of nuclear power plant, the seawater temperature change is bound to affect the safe and stable operation of the nuclear power units. The reactor coolant pump is an important equipment for the safe and stable operation of nuclear power units. It is necessary to analyze the impact of seawater temperature rise on its operation. The thermal barrier of the reactor coolant pump is designed to take away the heat from the reactor coolant side and ensure that the inlet temperature of the No. 1 shaft seal water of the reactor coolant pump is lower than the maximum value allowed by the design, so as to ensure the safe and stable operation of the reactor coolant pump. The design of the reactor coolant pump thermal barrier of CPR1000 unit takes into account the most severe operation condition of the complete loss of the reactor coolant pump shaft seal injection. Based on the measured operation data of a typical CPR1000 unit when the reactor coolant pumps completely lose the shaft seal injection, and using the FLOWMASTER software, the heat exchanger model of the reactor coolant pump thermal barrier is established. The impact of the cooling water inlet temperature of the reactor coolant pump thermal barrier rising from 35 to 40 °C on the performance of the reactor coolant pump thermal barrier is calculated and analyzed. The analysis results can provide guidance for the operation optimization of the same kind of reactor coolant pump for CPR1000 unit under the high temperature of seawater.