[Objective] The main driving factors affecting the spatio-temporal variation of water conservation on Hainan Island were analyzed in order to provide a decision-making basis for the identification and protection of key areas of water conservation function, water resource management, and regional sustainable development of the Hainan Island ecosystem. [Methods] Based on the water yield module of the InVEST model, the spatio-temporal changes in water conservation on Hainan Island from 1996 to 2020 were quantitatively analyzed, and a geographic detection and analysis of the influencing factors of water conservation on Hainan Island was conducted. [Results] ① The total amount of water conservation in Hainan Island increased slightly from 1996 to 2020. The annual average water conservation was 41.77 mm, and the total water conservation was 1.42 billion m³. Water conservation on Hainan Island was high in the east and north, and low in the west and south. Among all land use types, forest had strong water conservation capacity and accounted for a large area, making a significant contribution to the water conservation of Hainan Island. ② Water conservation had a strong positive spatial correlation, showing obvious aggregation characteristics. The key areas of water conservation were mainly located in the eastern and central parts of Hainan Island, the eastern coastal zone, and the volcanic lava wetlands to the west of Haikou City. ③ The influence of each factor on water conservation followed the order of precipitation>actual evapotranspiration>land use pattern>elevation. The interaction of factors, especially the interaction between precipitation and land use pattern, significantly enhanced the distribution of water conservation. [Conclusion] Climate and human activities dominated the spatial pattern of water conservation on Hainan Island. In the future, it is necessary to fully consider the impact of climate change on water conservation, establish effective measures to ensure that the water conservation function of the Hainan Island ecosystem can effectively adapt to global changes, and ensure land ecological security through rational utilization and management of land resources.