The water cycle in the tropical regions is the important driving force for the evolution of the global climate system,and Hainan Province is the only tropical island province in China,which is an ideal area for the study of tropical water vapor cycle.Hydrogen and oxygen stable isotopes in water are important method for water cycle research.In this study,the transport path and source of water vapor in Hainan Island are studied through the spatial distribution of stable isotopes of major rivers in Hainan Island.The isotopes of the river water of Hainan Island are gradually positive from west to east in the latitude direction,and are symmetrically distributed in the longitude direction.The isotopes of the southeastern river of Hainan Island show the"altitude effect",while the isotopes of the Changhua River in southwestern Hainan Island show the"anti-altitude effect".The spatial distribution of river water isotopes in Hainan Island shows that topography is the most important factor controlling the spatial distribution of river water isotopes,and the eastern part of Hainan Island is the windward slope of water vapor transport,while the west is in the"rain shadow area",and water vapor is transported from east to west.