This paper analyzed the main problems of remote islands on long- distance water supply from the mainland by shipping in typhoon-prone environment. The freshwater protection mode of self-sufficiency in situ was proposed. The features，complementarities，specific methods and technical means of water supply problems in situ of remote islands and reefs by two methods of rainwater harvesting and desalination by renewable energy power generation system were discussed. Research shows that the two specific fresh water supply modes of“the underground shallow lake rainwater harvesting system in coral sand beach”and“the reverse osmosis desalination systems powered directly by photovoltaic energy”have complementary and a high development potential，which are suitable for application in remote islands.