Fulong Spring, along K398–K402 in the Hezhou-Bama Highway’s Dahua section, was selected for hydrochemical monitoring. This study tracked 13 hydrogeochemical indices, including EC and 6 ions, at 7 sampling points from May 2019 to July 2020. The Piper and Gibbs graphical methods, along with statistical analyses, assessed hydrochemical types, spatiotemporal variations, and controlling factors. The key findings included: ① Fulong Spring has a pH ranging from 6.52 to 10.03 (average 7.22), indicating neutral to alkaline water with Ca2+ and Mg2+ as dominant cations and HCO3 - and NO3 - as principal anions. The hydrochemical type, Ca-HCO3, reflects the influence of carbonate rock. The water type at the Nongfa Tunnel entrance is Na-K-HCO3 due to tunnel construction drainage. ② Geochemical indicators in Fulong Basin show minimal seasonal variation, suggesting limited precipitation influence. The tunnel drainage area and Dangui Karst Window show significant spatial differences compared to other points. ③ Most sampling points, except the Nongfa tunnel, exhibit significant water-rock control with minimal precipitation and evaporation influence. However, in the Nongfa Tunnel, carbonate rock dissolution predominantly influences the hydrochemical characteristics. The Nongfa Tunnel is impacted by tunnel drainage and agricultural chemical fertilizer pollution, while the Dangui Karst Window exhibits agricultural fertilization-induced valley sink water contamination.