Landscape ecosystems of sea islands are undergoing drastic changes due to the combined effects of natural processes and anthropic activities. Fresh water is the foundation of sea-island life and the key constituent part of sea-island landscape ecosystem. The effect of anthropic activities on freshwater system is one of key topics of them on landscape ecosystems of sea island. As an isolated landscape ecosystem, almost the entire freshwater recharge of sea island comes from rainfall. The rainfall-intercepting capability is very important for maintaining the balance of fresh water of sea island. A number of studies suggested that landscape factors including cover type, soil group and treatment, obviously impacts on the rainfall-intercepting capability. Therefore, it is greatly significant to probe into the effect of landscape pattern on rainfall-intercepting capability of sea island and the quantitative relationship between them. Firstly, landscape patterns of Tantoushan Island in Xiangshan county, Zhejiang province, China, for 1966, 2004, and 2012 were produced through landscape identification and classification of multi-resource remote sensing KH-7 homochromatic, QuickBird multispectral, and WorldView-2 multispectral imageries, and contemporaneous historical data. Shrub and grass was consistently the dominant landscape class throughout the entire period. There were remarkable changes of landscape types and landscape area from 1966 to 2012. There was major loss of arable land from 1966 to 2004. Coniferous forest disappeared entirely from 1966 to 2004, and then reoccurred between 2004 and 2012. Broad-leaved forest appeared and expanded greatly from 1966 to 2004, then decreased slightly from 2004 to 2012. The area of bare rock and land showed an obvious increase, and shrub and grass showed a declining trend over the 46 years. Driving analysis indicated these drastic changes were caused by afforestation, changes in exploitation methods, human-induced fire and diseases, as well as natural succession. Then, based on a holistic viewpoint, the paper researched into the quantitative relation between landscape pattern of sea island and rainfall-intercepting capability by the example of Tantoushan Island, and developed a comprehensive index——Total Rainfall Loss Rate (TRLR) used to assess the effect of landscape changes on rainfall loss quickly. TRLR is a simple weighted sum of CN values representing the runoff potential of specific landscape types from the TR-55 runoff prediction model. The results showed a continuous rise in TRLR of Tantoushan Island from 1966 to 2012,which suggested a continuous decline of the rainfall-intercepting capability. From 1966 to 2004, 2012, area ratio of shrub and grass to the whole landscape ecosystem decreased from 80.18% to 66.43%,60.15%, which was the major cause leading to the decline of rainfall-intercepting capability of Tantoushan Island. This trend is bound to do harm to freshwater prism, and then threatens the whole landscape ecosystem of sea island. The variation in TRLR must receive enough attention, and the effective countermeasures should be adopted to keep and even enhance the rainfall-intercepting capability for the health and sustainability of Tantoushan Island. In view of the rainfall-intercepting capability of single landscape type, shrub and grass landscape might be a priority rather than broadleaved forest and coniferous forest in island restoration project.