<p>The fault network significantly impacts the evolution of groundwater hydrochemical in coal mining regions. In this study, the spatial evolution and primary controlling mechanisms of groundwater hydrochemistry in the Carboniferous limestone aquifer of Suntuan coal mine, North China were investigated through the integration of hydrochemical correlation analysis and fault complexity evaluation model. The results show that HCO₃⁻ and Cl⁻ are the dominant anions in the groundwater, while the cations show dispersive features. Furthermore, ion correlation analysis suggests that minerals dissolution and cation exchange between Na⁺ and Ca²⁺ are the dominant water-rock interactions. The calculation results of the fault complexity evaluation model constructed based on the AHP–entropy weight coupling method show that high values are banded along the NE direction and closely related to faults that traverse the study area, as well as at the intersection of two faults. The distribution pattern of principal component scores indicates that the dissolution of carbonate minerals decreases with the complexity of faults, while cation exchange exhibits the opposite behavior. The primary controlling mechanism of fault complexity on groundwater hydrochemical evolution mainly contributes to changes in groundwater hydrodynamic conditions, resulting in slower groundwater flow and longer contact time between ions and minerals, which inhibits the dissolution of carbonate minerals and promotes cation exchange. The findings of this work not only have important applications for the quantitative evaluation of geological structure and groundwater resource management in Suntuan coal mine, but also provide a research template for other coal mines in North China.</p>