Abstract: According to the investigational data of oil content in the surface water of Dongshan Bay from 2009 to 2011,the distribution character and pollution degree of oil in the investigational sea area were studied with single index method. Results showed that the measured values and the average values of oil content were below the standard values of first national seawater quality,and seawater quality all met the national standards. In terms of seasonal oil content,the sequence was autumn >winter >summer >spring,but no obvious change by years; in terms of region oil content,the adjacent water of the northern part of Dongshan Island and Tayu and the western part between Gulei Cape and Shanwei were most seriousty polluted,but the water between the mid-west part and forepart was the lowest.