In this paper,  the authors focuses on seawater-sediment-Sargassum system as research object and analyzes the geochemical and biogeochemical characteristics for Cu, Pb and As in the seawater, surface sediment, Sargassum and cells of Sargassum. The results show that the concentrations of Cu, Pb and As are lower than the values of grade Ⅰ national standards for sediment, but some are of high-value in some sampling sites because of the source of input. The results also provide the forepart warning information for ecological environment of Daya bay.