Aeolian-fluvial interactions are critical for sand transport along the piedmont of the southern Taklimakan Desert. Yet the role of fluvial processes and sediment provenance in this context remains insufficiently understood. This study investigates the respective influences of combined aeolian and fluvial processes on sand transport, focusing on pathways, distances and mechanisms. By integrating grain size and Rare Earth Element (REE) geochemistry with remote sensing, we examined transport processes along the southern margin and clarified the dual role of rivers at piedmonts. Results reveal significant spatial differences in sediment sources, depositional structures, and transport mechanisms. For coarse particles, the eastern sector is mainly supplied by the Eastern Kunlun and Altun Mountains, while the western region is influenced by both the Eastern and Western Kunlun Mountains. The analysis of eastern samples indicates a complex provenance controlled by multiple sources, whereas western samples reflect more stable depositional processes with a concentrated sediment source. Climbing dunes occur only in the eastern piedmont and are absent in the west; their formation is jointly controlled by wind speed and direction, and river orientation and discharge. Overall, sedimentary processes along the southern margin of the Taklimakan Desert exhibit strong spatial heterogeneity. Aeolian-fluvial interactions regulate sand transport and depositional structures, highlighting its pivotal role in shaping desert landscapes. This study deepens our understanding of aeolian-fluvial dynamics at desert margins and provides theoretical support for provenance analysis and dune evolution in arid environments.