With the continuous advancement of third-generation nuclear power technology, the application scenarios of small nuclear reactor platforms are expanding beyond coastal nuclear power plants. This paper designs an automatic radiological monitoring system for marine island scenarios to meet the radiation monitoring needs of nuclear power facilities in specialized application environments. The system aims to expand the scope of environmental radiation monitoring and enhance relevant standards. A typical island in the northern South China Sea was selected as the application scenario, and its meteorological and climatic conditions, as well as pollutant dispersion simulation results, were analyzed. Based on this analysis and drawing from the experience of terrestrial nuclear power environmental radiation monitoring systems, the design of the system includes components such as anti-rolling automatic weather stations, gamma monitoring station networks, unmanned mobile data acquisition systems, data communication networks, and environmental monitoring central stations. The system also utilizes domestic environmental dose detectors and microcontroller unit data acquisition systems, and the entire set of application software was developed independently. Continuous operation tests were conducted in a coastal area in South China. After 198 days of continuous operation, the system demonstrated stable performance with a data acquisition rate exceeding 99%. The monthly average of the 60-second average dose rate was around 100 nGy/h, consistent with normal background radiation levels. The meteorological data showed consistent trends when compared with the local meteorological bureau's standard weather station, proving to be reliable and stable. The test results demonstrate that the system can meet the radiation monitoring needs of nuclear power facilities in island environments and is stable, reliable, and suitable for specialized maritime environments.