Exploring ecosystem services, trade-off synergistic relationships, and their driving mechanisms is the basis for scientific management of natural resources and ecologically rational planning, and has importantly theoretical significance for effectively enhancing regional ecological, economic and social benefits, and human well-being. The coastal protection forest is an important coastal green ecological barrier in China, which is one of ten major ecological barriers and major ecological restoration projects being built in China. Using this area as the study area, we investigated the service quantities of carbon sequestration, soil conservation, and water production in the region based on the RUSLE model, InVEST model method, and analyzed the synergistic relationships and driving mechanisms based on Pearson correlation coefficient method, so as to provide reference for formulation of reasonable ecological construction plans in coastal areas and is essential for improving the ecological situation in coastal areas as well as promoting sustainable economic and social development in coastal areas. The results of the study showed that: (1) the overall level of ecosystem services in the Coastal Shelter Forest System Construction Project (CSFSCP) increased between 2000-2020, and the best ecological construction effect was achieved in the second phase. Temporally, the CSFSCP project increased the overall ecosystem service capacity by 10.63% between 2000-2015 and decreased the overall ecosystem service capacity by 19.33% between 2016-2020. Spatially, ecosystem services increased significantly in the area south of the Yangtze River. (2) The overall synergistic relationship between ecosystem services in the whole region between 2000-2020 was dominant, with significant synergy between soil conservation and water production. The overall level of synergy between ecosystem services was the highest in the second phase of CSFSCP construction. Among these, the correlation coefficient between carbon sequestration and soil conservation was 0.06, soil conservation and water production was 0.68, carbon sequestration and water production was 0.02. (3) The scale effect of the relationship between ecosystem services in the construction sub-region and construction sub-region existed mainly in soil conservation and water production. Soil conservation and water production were significantly synergistic across the region and building sub-region, with significant trade-offs in the building sub-region; carbon sequestration and soil conservation were synergistic across the region with significant synergies in the building sub-region. (4) There was spatial and temporal heterogeneity as well as complexity in the drivers and driving mechanisms affecting inter-ecosystem relationships in the four CSFSCP construction zones. The degree and direction of influence of different drivers on the trade-off synergistic relationships varied from region to region. The trade-off synergy was mainly influenced by meteorological factors in the north, vegetation and topographic factors in the south, and the impact of human activities on the trade-off synergy was mainly negative, with spatial heterogeneity in the driving factors.