[Objective] Compared with naturally formed tropical coral islands，newly formed coral islands develop dense layers within their profiles due to hydraulic filling and sedimentation during the construction process. This study aims to investigate the effects of the hydrological properties and hydrological conditions of coral sand profile structures on hydrological processes such as slope water drainage，subsurface runoff，and coral sand particle transport. [Methods] Taking the dense layers in the profile of a newly formed coral island as the research object， in-situ profile surveys and sampling were conducted to analyze the texture types and hydro-physical properties of the coral sand profile. Combined with laboratory-simulated rainfall experiments，the hydrological process and coral sand loss characteristics on slopes with homogeneous layers and dense layers under different hydrological conditions were analyzed. [Results] Coarse coral sand exhibited strong hydraulic conductivity，while the dense layer had poor hydraulic conductivity，with a saturated hydraulic conductivity only 8% of that of other coral sand texture types. On slopes with homogeneous coral sand，all rainfall infiltrated through leaching，with no surface runoff. In contrast，the dense layer retarded water migration to deeper layers，causing subsurface runoff as the main form，accounting for about 87% of total rainfall and leading to particle transport and loss within the coral sand body. At the same time，changes in hydrological conditions，from free drainage to saturation and seepage， could promote subsurface runoff and coral sand loss，but a dense layer with low hydraulic conductivity could reduce coral sand loss under seepage conditions. [Conclusion] Dense layers can significantly alter the freshwater hydrology and sand particle loss of coral sand， potentially leading to effects such as shallower freshwater circulation and the development of dissolution fissures in localized areas. These results are of great significance for understanding the circulation process of coral islands and for the construction of ecological islands.