Abstract: During the dry and rainfall periods of 2005 to 2006, fieldwork measurements and laboratory measurement were used to determine the environmental factors from seven monitoring stations in three transects, including salinity, Oil, pH, inorganic nitrogen(NO₂-N, NO₃-N, NH₄-N), inorganic phosphorus(PO₄-P), active silicate(SiO₃), DO, COD, chlorophyll. a, and coliformin. The results showed that water quality in Sanya Bay was a measure of recognition and sized up the requirement of ocean function divisions. As affected by terrestrial resources, the water quality was relative poor in the number 1 station which was close to the Sanya Bay and the Sanya River estuary. And the measured values of nutrients, COD, coliformin were higher in coastal than that of pelagic ocean, and higher in the South than the West Bay. Furthermore, the water quality in Sanya Bay was significantly affected by Sanya River.