Abstract: Water quality was affected by the quick development of coastal tourism and aquaculture of Sanya City in recent years. Some water quality parameters of pH value, dissolved oxygen, phosphate, nitrite, total phosphorus and chemical oxygen demand were measured in coastal water of Sanya Bay, close to urban district, and Yalong Bay, far from urban district, from January to April in 2013 for assessment of water quality of coastal water of Sanya City. Concentrations of phosphate, nitrite, total phosphorus and chemical oxygen demand of coastal water of Sanya Bay were higher than that of Yalong Bay, and there were significant difference （P〈0.05） and very significant difference （P〈0.01） in some months. Value of pH and dissolved oxygen of both bays indicated that water quality of both bays were consistent withⅠ-Ⅱkind sea water quality standards. Phosphate concentration of Sanya Bay and Yalong Bay were 0.015 2-0.018 9 mg/L and 0.008 2-0.014 3 mg/L respectively, which were consistent withⅡ-Ⅲkind andⅠsea water quality standards, respectively. Chemical oxygen demand of Sanya Bay and Yalong Bay were 0.528-0.899 mg/L and 0.533-1.013 mg/L respectively, and both were consistent with Ⅰsea water quality standards. Water quality of coastal water of Yalong Bay was better than that of Sanya Bay, and water quality of former was consistent withⅠkind sea water quality standard in most coastal water area, and the latter was consistent withⅡ-Ⅲkind andⅠkind sea water quality standard in most coastal water area and part coastal water area respectively, in tourism season.