Abstract: This paper introduces the two main cooling methods of the current coastal nuclear power plant: once-through cooling and secondary circulation cooling, as well as their characteristics, advantages and disadvantages. It analyzes the differences of the drainage engineering of the two cooling methods, including subsurface pipe drainage and open channel drainage, and discusses the advantages and disadvantages of each type of drainage system. Combined with the cooling method and drainage scheme comparison and optimization case of Shandong a nuclear power project, this research demonstrates that adopting a secondary circulation cooling system significantly reduces the volume of warm water discharge compared to the once-through cooling method. Specifically, the area of 4 °C temperature rise envelope is only 3% of the sea area of once-through cooling scheme, which not only reduces the sea area of the temperature drainage significantly, but also greatly reduces the nuclear power withdrawal drainage. It not only greatly reduces the sea area use for warm water discharge, but also greatly reduces the loss of marine life. This approach aligns with the project's requirements for efficient and economical use of the sea. Therefore, the adoption of secondary circulation cooling and optimized drainage engineering in coastal nuclear power plants can effectively mitigate the impact on marine ecosystems, promoting harmonious development between the economy, society, and the environment.