Abstract: With increasing global restrictions on per- and polyfluoroalkyl substances (PFAS), the production of PFAS precursors as alternatives has been growing. Among these, 6∶2 fluorotelomer sulfonic acid (6∶2 FTS), as one of the most prevalent precursors, has been widely detected in groundwater systems and is associated with contaminant transport and migration, making it a pollutant of significant concern. Current research lacks in-depth investigation into the key retardation mechanisms, failing to bridge experimental observations with microscopic mechanisms. This results in an absence of atomic-level mechanistic analysis of transport phenomena and an inability to accurately predict environmental behavior of contaminants. In this study, miscible displacement experiments were conducted to simulate typical hydrogeological conditions in saturated and unsaturated zones of groundwater systems, elucidating the transport behavior of 6∶2 FTS at the macroscopic scale. Density functional theory (DFT) calculations were employed to unravel the microscopic adsorption mechanisms of 6∶2 FTS at both solid-phase (quartz sand) and air-water interfaces at the atomic scale. A multi-scale approach integrating microscopic and macroscopic perspectives was adopted to analyze the environmental behavior of 6∶2 FTS. The results demonstrate that 6∶2 FTS migrates rapidly in saturated sand columns, while under unsaturated conditions, its breakthrough is significantly slowed due to pronounced contributions from air-water interface adsorption. The mean retardation factor increases from 1.085 to 1.971. DFT calculations corroborate these findings, showing that the adsorption energy of 6∶2 FTS at the air-water interface (−2.63eV) is substantially lower than that in the quartz sand system (−0.95eV). In subsurface (aqueous) environments, 6∶2 FTS predominantly exists in its ionic form. The dominant adsorption configurations reveal that hydrogen bonding between O atoms of 6∶2 FTS functional groups and surface H atoms serves as the primary driving force for adsorption. Additionally, due to attraction from surface H atoms, the S–O bonds in the functional groups exhibit slight elongation. This study provides a comprehensive analysis of the environmental behavior of 6∶2 FTS in groundwater systems across both microscopic and macroscopic scales. The findings offer a scientific basis for assessing its contamination potential in groundwater systems and establish a theoretical foundation for further large-scale modeling. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202504080082.