The Yinggehai-Jiusuo Basin is located within the South China Plate and situated near the Jianfeng-Diaoluo Fault( F1 ) and the Jiusuo-Lingshui Fault ( F2 ) . It boasts abundant geothermal resources, which are extensively distributed in the sedimentary sand layers of the Yinggehai-Jiusuo Basin and granite fractures. To resolve the issue of insufficiency in regional sedimentary basin-type geothermal research, 43 hydrochemical samples and 27 hydrogen-oxygen isotope samples were collected. Combined with ion ratio calculation, PHREEQC-based mineral saturation index simulation, cation geothermometer, SiO2 geothermometer, and the silicon- enthalpy graphic method considering maximum steam loss, a systematic analysis was conducted on the hydrochemical characteristics of geothermal water, laws of material cycling and genetic model. The results show the following. The hydrochemistry of geothermal water exhibits significant spatial and vertical differentiation. From the bedrock area to the southern part of the basin, the hydrochemical type transforms from HCO3 -Ca·Na to SO4·HCO3 -Na, and the average concentration of F - increases from 0. 5 mg / L to 10. 2 mg / L. Vertically, the contents of TDS, Na + , and Cl - in geothermal water from Yinggehai decrease with depth, while those in Jiusuo show an increasing trend. The hydrochemical components are mainly controlled by rock weathering, with poor overall confinement. Cations are subject to dual regulation by the leaching of silicate minerals and cation exchange adsorption,where Ca2 + and Mg2 + displace Na + and K + in minerals. The enrichment of F - is the synergistic result of fluorite dissolution, calcite precipitation promoted by an alkaline environment, and the combined action of the Jianfeng-Diaoluo Fault ( F1 ) and Jiusuo-Lingshui Fault ( F2 ) . The silicon-enthalpy graphic method is preferred for calculating geothermal reservoir temperature, with a range of 84 ~ 234 ℃ . The temperature is the highest in the Fubao Qianjia geothermal field ( 167 ~ 234 ℃ ) and the lowest in the Yinggehai geothermal field ( 84 ~ 96 ℃ ) . Geothermal water originates from atmospheric precipitation, with a recharge elevation ranging from 513 m to 977 m, showing a variation pattern of “ bedrock area > the northern part of the basin > the southern part of the basin ” . A geothermal genetic model was established: high-altitude precipitation infiltrates along F1 and undergoes deep circulation. After being heated by Yanshanian granite and undergoing water-rock interaction, it differentiates to form bedrock fracture-type geothermal reservoirs and basin layered-banded composite geothermal reservoirs. With the superposition of the F2 fault, the Jiusuo high-F - composite geothermal reservoir is formed. Based on the calculated geothermal reservoir temperature and measured hydrochemical characteristics, the zoning of geothermal resource development potential was carried out. The research results can provide theoretical support and practical reference for the exploration, development and utilization of similar sedimentary basin-type geothermal resources in the coastal areas of South China.