During the spring thawing period, soil detachment under snowmelt runoff is significantly influenced by the alterations in soil structure due to freezing-thawing effects and the occurrence of subsurface seepage. To explore the mechanism underlying the interactive effects of freezing-thawing and subsurface seepage on detachment rate of Mollisol, soil tanks underwent a series of freezing-thawing treatments, and the shear strength (Ss) and detachment rate (Dr) were measured under subsurface seepage conditions. Pore structure and aggregate characteristics were quantitatively analyzed using a 25-mu m resolution industrial CT and dry or wet sieving, respectively. Partial least squares regression (PLSR) was employed to examine the relationships between soil structure characteristics and the Ss. Findings indicated that freezing-thawing effects significantly altered pore structure and aggregate characteristics. The Dr increased as the Ss decreased under freezing-thawing effects, closely linked to soil structure characteristics. Soil structure characteristics, including the porosity (>= 80 mu m), the proportion of dry aggregates (excluding 2-1 mm), the proportion of water-stable aggregates (5-2 and 1-0.5 mm), mean weight diameter, and fractal dimension of dry aggregates, were identified as the primary factors influencing the Ss. Pore structure and aggregate characteristics accounted for 89.5% of the variation in the Ss. The occurrence of subsurface seepage significantly diminished Ss, exhibiting a negative power relationship with the Dr. The findings advanced the understanding of the generation mechanism of snowmelt erosion in response to the interactive effects of freezing-thawing and subsurface seepage during the spring thawing period.