The global ocean water temperature continues to rise. As the final cold source of the core heat of CPR1000 unit, the temperature change of sea water will inevitably affect the safe and stable operation of the unit. This paper studies and analyzes the design and operation characteristics of the nuclear island system of CPR1000 unit, and carries out technical research from the perspective of design basis, heat exchange performance analysis of nuclear island equipment and operation. Based on the analysis results, the optimization of high temperature operation of seawater is proposed to provide guidance for the safe operation of nuclear power plant.