Abstract: The coastal tourism in Sanya city has developed in recent years, and coastal waters environment was affected. Some water quality parameters of pit, dissolved oxygen, nitrite, phosphates, total phosphorus and chemical oxygen demand were measured for evaluating the water quality affected by different coastal tourism activities from January to April in 2013 in Yalong Bay. Results showed as followed： concentration range of dissolved oxygen was 6.3-7.4 mg/L and the comparison of that was control area〉swimming area〉living area〉speed-boat cruising area （P〉0.05）.Concentration range of nitrite was 0.003 8-0.005 7 mL/L and comparison of that was speed-boat cruising area 〉swimming area 〉living area〉control area,furthermore ,there was significant difference for the concentration of nitrite between speed-boat area and controlling area（P〈0.05 ）. Concentration ranges of phosphates and total phosphorus were 0.007 5-0.012 7 mL/L and 0.011 4-0.062 7 mL/L respectively, and the comparison of that was speed-boat cruising area 〉 living area 〉swimming area 〉control area,in addition ,concentration of both was higher significantly in speed-boat cruising area than that in controlling area and swimming area （P〈0.05）.Concentration range of chemical oxygen demand was 0.48-1.28 mL/L and the comparison of that was living area〉speed-boat cruising area〉swimming area〉control area （P〉0.05）.Conclusions were as followed： water quality of Yalong Bay was accordance with Ⅰ water quality standards overall in tourist rush season, but meets Ⅱ water quality standards in specific months because of the impact of different coastal tourist activities. Activities of speed-boat cruising and living area had more influence than other coastal tourist activities in coastal area of Yalong Bay in tourism rush season.