22 annual layered samples of coral from 1977 to 1998 were collected from Daya Bay, South China Sea, their bomb-14C(nuclear weapons testing 14C) concentrations were determined and studied, and the atmosphere-sea exchange rate and diffusion thickness were estimated and found to be 17 mol·m-2·a-1 and 32 μm, respectively. The interannual variation of coral △14C is mainly controlled by oceanic factors. In ENSO years, the coastwise upwelling current of South China Sea gets intensified, hence the coral △14C displays its bottom value. The coral △14Cdoes not respond vividly to the variation of the solar radiation energy. In thepast 20 years or so, the general situation and the oceanic thermal structure ofSouth China Sea are still stable even though interannual variation occurs in the atmosphere-sea interaction and the upwelling current driven by the tropical energy.