【Objective】Aeolian dust deposition constitutes a major source of fine particles in many high-mountain surface soils worldwide. However, systematic quantitative research on the specific sources and transport mechanisms of fine-grained matter in high-altitude soils of the Qilian Mountains along the northeastern edge of the Tibetan Plateau remains limited. This study combines grain-size distribution characteristics with end-member modelling analyses (EMMA) to reveal the eolian origin and transport pathways of soils in the Qilian Mountains. 【Method】This study collected 6 weakly developed loess-like soil profiles at the mountain front and 81 representative alpine soil profiles from high-elevation zones across the Qilian Mountains. Grain-size distributions of all samples were measured using a laser particle-size analyzer. EMMA was applied to unmix grain-size distribution curves and extract statistically robust sedimentary components. By integrating the spatial distribution patterns of each end-member with the influence of environmental factors, sediment sources and transport processes were analyzed. 【Result】The measured grain-size distributions of both loess and alpine surface soils exhibited remarkably similar patterns and shared a consistent dominant peak at approximately 37 μm. This similarity indicated common sediment sources. C horizons and even coarse, polymodal 2C layers retained this distinctive component, indicating pervasive penetration of aeolian dust throughout soil profiles. EMMA resolved five environmentally meaningful end-members (EM1-EM5), representing distinct transport and depositional processes. EM3 (~33 μm) dominated and was predominantly distributed on the northwestern side, showing significant negative correlations with elevation, precipitation, and vegetation cover. EM2 was widely distributed throughout the study area and showed a significant positive correlation with precipitation. EM1 was predominantly distributed in the southwest region, showing a positive correlation with elevation, precipitation, and vegetation cover. 【Conclusion】Fine-grained alpine soils in the Qilian Mountains are predominantly derived from aeolian dust. Fine fractions (EM1, EM2) are associated with long-range transport under the prevailing westerlies, whereas coarser silt components (EM3) correspond to stronger winter monsoon activity and shorter-distance transport. Continuous aeolian deposition forms distinctive lithologic discontinuities that substantially modify soil physical and chemical properties, thereby influencing nutrient dynamics, ecosystem productivity, and long-term stability of alpine pastoral systems. These findings highlight the fundamental ecological and geomorphological importance of dust deposition in shaping high-elevation soils on the northeastern Tibetan Plateau.