Abstract: To meet the request of rapid development of China’s coastal nuclear power plants, it is important to improve China’s marine nuclear emergency preparedness and response capability. This paper proposes a modular, componentized and objectoriented marine radioactivity monitoring and early warning technical support platform based on the properties and working contents of national marine radioactivity monitoring. The system platform relies on computer software, hardware and network communication. It can perform the daily supervision on the marine environment of the coastal nuclear power plant, simulate and study the migration and diffusion of radioactive liquid effluents in the marine environment, formulate the maritime emergency monitoring plan, review and evaluate the marine radioactivity monitoring data and carry out the marine bioradiation risk assessment. The construction and operation of the system can provide technical support for marine nuclear accident emergency monitoring, enhance the marine nuclear emergency management and command decisionmaking in China.