As a unique type of ecosystem, tropical coastal sandy vegetation lies in the transition zone extending from coastal beaches to further inland and provides important ecosystem services such as windproofing, tourism, and agriculture. However, the energy and matter fluxes of these tropical coastal ecosystems have been rarely studied. We reported one-year eddy flux observations in a tropical sandy coastal ecosystem and specifically focused on the carbon and water exchanges between the atmosphere and the ecosystem. The studied ecosystem was a carbon sink (approximately –560 gC m−2 yr−1) and approximately 1000 mm of water evaporated from the ecosystem into the atmosphere during the study year. The highest levels of vegetation photosynthesis occurred in April, shortly before the wet season. This can be attributed to an endogenous self-adjustment of the ecosystem to improve the water- and carbon-use efficiency during the wet season. This study is expected to not only fill the data gap with respect to the gas exchange between tropical sandy coastal plains and the atmosphere but also provide knowledge about the function and ecological service of these specific ecosystems.