Water resources shortage in Dongting Lake is increasingly serious, which has become an important limited factor for economic development in the Dongting Lake basin. The Dongting Lake eco-economic zone was selected as the research object, and the Synergistic Evaluation Model of water resources and socio-economic system in the 26 counties of the economic zone was constructed with the help of synergy theory and set pair analysis (SPA) method. The results showed that the overall synergy degree between the two systems in the eco-economic zone is not high, and the synergy degree among the counties is obvious. Among them, the water resources and socio-economic systems in Li County, Linli County, Taoyuan County, Shimen County, Heshan District, Yuanjiang City, Datonghu District, and Taojiang County have a high synergy degree. However, the synergy degree of Linxiang City and Yueyang County is relatively low, and other counties are at a moderate level of synergy. It was found that the degree of coordination between the water resources and the socio-economic system is determined by the degree of stability of water resources system; therefore, the potentiality of the water resources development and utilization in the economic zone is great. Finally, the solutions and suggestions to promote the coordination between water resources and socio-economic system were provided.