Off-shall seawater in China was often polluted and eutrophicated more or less because of human activities. The ecosystem services could be incorporated into the decision-making process by managers only if the ecosystem services were economically marked. Therefore, it was important to evaluate the value of ecosystem service (VES) and service value loss due to marine pollution and eutrophication. Taking Haizhou Bay as the study area, the potential and actual economic values of marine ecosystem were evaluated. The assessment results showed that the total potential value of ecosystem service of Haizhou Bay was 16.64 ×10⁸ Yuan in 2005, with an average unit VES of 1.90×10⁶ Yuan/km². Within the total potential VES, the provision services, culture services, and regulation services accounted for 53.39%, 35.48%, and 10.84%, respectively. Considering the service loss due to red tide, greenhouse gas emission, and pollutant accumulation in fish, alga, and shellfish, the actual VES was 14.08×10⁸ Yuan in Haizhou Bay, with the average of 1.61×10⁶ Yuan/km². The value of provision services, culture services, and regulation services accounted for 48.32%, 41.94%, and 9.74%, respectively, in total actual VES. The VES loss due to the eutrophication and seawater pollution was 2.56×10⁸ Yuan, accounting for 15.41% of the potential VES. The deterioration of the marine environment greatly influenced the services of food provision and climate regulating at present. Moreover, the values provided by other services, such as tourism, would decrease if the marine environment is further deteriorated. Compared with the averaged service value of marine ecosystem in other areas of China, the VES in Haizhou Bay was relatively low. This indicated that there existed a big improvement space for development and utilization of ecosystem services in the study area. However, it could not be neglected that the development brought the ecosystem deterioration and decreased the marine ecosystem services in bay area, and it needs to trade off the benefit from development and the loss due to deterioration caused by human activities.