The sources of sulfate and its migration characteristics associated with lacustrine groundwater discharge (LGD) in lake-groundwater systems influenced by mining activities remain incompletely understood. Hydrochemical analysis, isotopic tracers (delta D/delta 18O/delta 34SSO4/delta 18OSO4/222Rn) and multi-isotope coupling models (Bayesian isotope mixing model and 222Rn mass balance model) were utilized in this study to reveal the sources and migration characteristics of sulfate in the lake-groundwater system of the Caojiatan Coalfield. The results show that water bodies in the mining area are dominated by weakly alkaline fresh water, and the hydrochemical types show a trend from the HCO3-Ca to SO4-Ca types. In phreatic and confined groundwater, sulfate is primarily derived from gypsum dissolution (21.20 % and 18.80 %) and pyrite oxidation (25.75 % and 32.95 %), respectively. The calculated LGD rates range from 1.97 to 16.84 mm/d, accompanied by substantial SO42-fluxes (59.69-510.25 mg/m2/d). Lake L2 has a LGD rate of 16.84 mm/d (2-8 times that of other lakes) due to mining-induced fracturing of the lakebed strata. The methodology and findings of this study will aid in developing management strategies to protect water quality and provide references for studies on sulfur cycling in mining districts.