Abstract: Changes in wetland ecosystem structure and function are closely related to wetland ecological vulnerability and high-level ecological services. At present, however, few studies have explored the ecological losses caused by changes in wetland ecosystem structure and function. Based on the accurate registration and interpretation of a topographic map of Haikou from 1959 and image data from year of 1976, 1985, 1995, 2005, and 2018, we developed an ecosystem service value (ESV) method based on the equivalent factor, constructed an assessment model of the impact of changes in wetland ecosystem structure and function on ESV, and analyzed dynamic changes in wetland ESV. Results showed that: (1) from 1959 to 2018, ESV decreased by 1.073 billion yuan. From 1959 to 2018, only the ESV supply service increased by 58 million yuan, whereas the adjustment, support, and culture services decreased by 509, 187, and 47 million yuan, respectively. (2) Based on the revised ESV equivalent of the dynamic ESV model, only shallow waters, silty beaches, and mariculture farms showed an increase in ESV; wetlands/inland tidal flats, freshwater lakes, rivers, and reservoirs showed considerable losses in the ESV equivalent; freshwater farms, agricultural ponds/pit ponds, paddy fields, and other land types showed relatively light losses in the ESV equivalent; construction land showed a continuous decrease in the ESV equivalent. (3) Spatial scale differences were found in the assessment of wetland ESV, indicating that the self-regulation and restoration ability of a wetland cannot be ignored, and the threshold value of wetland ecosystem service function change under external disturbance needs to be further studied.