It is an important method to evaluate the loss of marine ecosystem service caused by marine reclamation from the sea, in order to allocate marine resources and regulate development of coastal economy and environmental protection. The traditional method of economic evaluation has some shortcomings, such as partially stressing the loss of economic benefit and ignoring the characteristics of ecosystem service including public goods properties, ineradicable externalities and difficulty of monetization for non-market part. These shortcomings will be modified by the emergy analysis which could illustrate the real wealth of ecosystem service by standardizing and accounting the energy and materials invested directly and indirectly from both natural environment and human society. In the present study, emergy estimating model was developed and based on the structural and functional characteristics of gulf ecosystem to evaluate the loss of ecosystem service caused by marine reclamation, which includes 4 categories of ecosystem function in detail such as Provision (i.e. food production, raw materials), Regulation (i.e. climate regulation, waste treatment, disturbance regulation), Support (i.e. nutrient cycling, biodiversity support) and Culture (i.e. research & education, tourism & recreation).The marine reclamation in the Taozi Bay, Yantai City, was presented as a case in the paper, which includes the fishing port project of Yantai Development Zone and the first and second phase projects of Dayu Shipyard. Results showed that the total loss of functional service was 3.32×10²⁴ sej per year, and the loss summarized by emdollar value was 2.28×10¹⁴ yuan during the whole lifetime (50 years) of sea area utilization, and the average loss of emdollar value was 1.73×10¹² yuan per hectare. The functional category of provision absolutely dominated the loss due to high intensification and solar transformation of the shellfish culture in original waters, followed by supporting service, regulating service and cultural service. In detail, the direct loss of emdollar value of food production was about 4.56×10¹² yuan per year in specific sub-function category, and the loss of biodiversity support and disturbance regulation was about 5.39×10⁷ yuan per year and 1.58×10⁷ yuan per year, respectively. The estimated emdollar value was significantly higher than the ecological compensation results1.41×10⁷ yuan according to the "Construction Projects on the Marine Biological Resources Impact Assessment Technical Regulations", which demonstrated that the current ecological compensation method underestimated the total loss of ecosystem service and partially reflected the effect of marine reclamation on gulf ecosystem. It is urgent to improve the evaluation method in order to effectively inhibit the unrestricted reclamation and protect the gulf environment. The successful evaluation in the case using the emergy model demonstrated some advantages. Firstly, it is capable of supporting the cumulative impact assessment at both the temporal and spatial scales. Secondly, it can be used to compare the emdollar value with the current monetary result based on the traditional economic valuation method. Thirdly, it has a wide application to evaluate the ecological cost happened in various sea-related construction projects, such as port, scenic spot, oil platform. Therefore, the compensation for utilization of offshore environmental resource, economic institution-building for reclamation control and sustainable development in coastal regions would be evaluated scientifically. However, the model still need to be improved in some aspects including the reasonable selection and calculation of solar transformation, the evaluation method of cultural service loss, and the dynamic simulation of the service loss before and after reclamation.