Fluvial-aeolian interactions are integral to the evolution of desert landscapes, yet the associated processes and sediment sources remain an area of active investigation. Recent studies highlight the potential of grain shape characteristics as indicators of sediment transport history and provenance. The Horqin Sandy Land (HQ) in northeastern China is a dunefield characterized by intensive fluvial-aeolian interactions. However, surface processes and its provenance connection with the upwind Hunshandake Sandy Land (HSDK) require further clarification. The grain size and shape of fluvial sediments and dune sand samples from the HQ and surrounding regions were analyzed to elucidate transport processes and sand provenance. The grain shape of most river sediments significantly differs from that of aeolian sands in the HQ, except for sediments from the Xilamulun River (XLML), which originate in the HSDK and exhibit grain shape characteristics similar to HQ aeolian sands. Approximately 80 % of the fine sand transported by the XLML is derived from the HSDK, resulting in high sphericity of finer sand in the western HQ. Aeolian sands in the HQ exhibit pronounced spatial heterogeneity in grain size and shape parameters, reflecting strong fluvial-aeolian interactions. Wind-driven sorting and abrasion exert dominant control on sediment patterns in the western and central HQ, while their impacts are diminished in the eastern HQ due to a barrier effect of rivers and increased sediments influx from the Yanshan Mountains. These findings highlight the complexity of fluvial-aeolian sediment dynamics. Moreover, they demonstrate that grain-shape analysis-characterized by low cost and high efficiency-can effectively resolve sediment provenance and surface processes even when their geochemical signatures are similar, underscoring its unique value as a tracer in desert environments.