Abstract: With the phase-out of traditional perfluoroalkyl acids (PFAA), production and use of alternatives, including PFAA precursors, have increased significantly. However, current research on these precursors primarily focuses on identification and biodegradation, with limited understanding of their soil transport mechanisms. This study investigated the interfacial adsorption behavior and transport characteristics of 6:2 fluorotelomer sulfonic acid (6:2 FTS), a representative PFAA precursor, at both air-water and solid-water interfaces through surface tension measurements and miscible displacement experiments, with particular emphasis on the effects of soil particle size, organic matter content, and water saturation.. The results demonstrated that the transport behavior of 6:2 FTS exhibitd strong water saturation-dependence: Under saturated conditions, retardation effects were relatively weak with limited contributions from solid-phase adsorption. In contrast, under unsaturated conditions, transport retardation was significantly enhanced, with air-water interface adsorption accounting for 61%-98% of total retention. Soil properties significantly influenced transport: Smaller particle size increased R from 1.7 to 2.8, while lower organic matter raised R from 1.7 to 3.7. Surface activity of 6:2 FTS surpassed perfluorooctanoic acid (PFOA) and ammonium perfluoro 2-methyl-3-oxahexanoate (GenX), highlighting its enhanced interfacial affinity. This study provides the first dataset on interfacial adsorption of 6:2 FTS in soils, critical for predicting its environmental fate.