Abstract: In order to assess the marine environmental quality around Qilianyu Island in the South China Sea， 22 surface seawater samples and 6 surface sediment samples were collected in August 2017. The contents of heavy metals including Cu， Pb， Zn， Cd， Cr， As and Hg were determined by atomic absorption spectrophotometer and atomic fluorescence spectrophotometer. The levels of heavy metal pollution in surface seawater were evaluated by single factor method， comprehensive pollution index and correlation coefficient. The pollution levels and the potential ecological risk of heavy metals in sediments were evaluated by the single factor method and Hankanson potential ecological risk index. The results showed that the concentrations of heavy metals in surface seawater were in sequence of C_Zn＞C_Pb＞C_As＞C_Cr＞C_Cu＞C_Cd＞C_Hg. The Pb quality in seawater of some stations was no better than the first grade by the national standard of seawater quality， but by the comprehensive pollution index it was less than 1， which means that the surface seawater quality around Qilianyu Island could be taken as clean. Statistically significant negative correlations existed between ZnAs and CrCd in surface seawater, which suggested that these two groups of elements were from different sources. The contents of heavy metals in surface sediments conformed to the first grade by the national standard of marine sediment quality. The potential ecological risk index for heavy metals in this area was low accordingly．