Marine nitrogen cycle and its transition control primary production, and therefore contribute to the concentration of atmospheric carbon dioxide, which is the essential information to understand the biogeochemical cycle and the global climate system. However, the spatial and continuous observation of nitrogen dynamics at surface ocean has been scarce. Reef coral skeleton could be used to reconstruct past nutrient dynamics in tropical and subtropical ocean with decades to millennia. Nitrogen isotope of organic matter in the coral skeleton could vary with change in nitrogenous sources and mainly capture nitrogen isotopes of marine nitrate. In this paper, I reviewed the progress of nitrogen isotope proxy in reef coral skeletons together with the introduction of our studies. Nitrogen isotopes in reef coral skeletons can be a high-resolution recorder of nitrate dynamics in oligotrophic ocean.