［Objective］ This study aims to reveal the spatiotemporal distribution patterns and driving mechanisms of fluoride in the wetland water of the Xianghai National Nature Reserve， clarify the reasons for water quality exceeding the standards， provide theoretical support for the scientific formulation of ecological governance measures for the Xianghai wetland， and offer guidance for regional water environment governance and improvement of water quality in the basin. ［Methods］ Based on the long-term monitoring data of the national control section of the surface water in the Xianghai Nature Reserve from 2012 to 2021， different concentration characteristics of fluoride in the flood， normal water， and dry seasons were compared to clarify the interannual and seasonal variation characteristics of fluoride. Pearson’s correlation analysis was used to explore the correlations among various water quality indicators， and a Gibbs diagram was compiled to analyze the chemical characteristics of the surface water and interpret the natural sources of fluoride. ［Results］ ① From 2012 to 2021， the annual average fluoride concentration in the surface water of the Xianghai Reservoir ranged from 2.02 to 3.87 mg/L， chronically exceeding the class Ⅴ surface water quality standard （GB 3838—2002） by 0.36—1.61 times annually. ② Temporally， fluoride concentrations were higher in the dry season （3.54—3.66 mg/L） and lower in the wet season （2.76—2.87 mg/L）， exhibiting an initial decline， subsequent rebound， and final decline， with pronounced seasonal fluctuations. Spatially， concentrations at Yichangpao （1.56—3.20 mg/L， 2022） significantly exceeded those at Erchangpao （1.16—2.48 mg/L）. ③ The average content of total fluoride in the soil within the surrounding area of Xianghai Reservoir ranges from 1，013.91 to 2，067.12 mg/kg， and the water-soluble fluoride content reaches 10.45 to 50.12 mg/kg， which is much higher than the national background value. ④ The dominant hydrochemical types of surface water were HCO₃⁻-Na ∙ Mg and HCO₃⁻-Na， with fluoride enrichment being closely linked to regional evaporation concentration， dissolution-precipitation， and ion exchange processes. ［Conclusion］ Endogenous release is the primary pollution pathway for fluoride in the surface water of the Xianghai reservoir. Control measures should focus on endogenous pollution management and hydrological regulation.