Mountain rivers are generally featured by deep-cut river valley and steep side slopes, which is prone to landslide-dammed lake and outburst floods. Taking 2018.10.10 Baige landslide-dammed lake in Jinsha river as an example, wind reworked the outburst flood sediments and developed a plenty of sand dunes at the bank of Jinsha river. This studies about aeolian dunes in the Yarlung Zangbo River, to some extent, could provide some implication for the sedimentary distinction of aeolian sand and original flood deposit, and has some significance for engineering control of aeolian dune in this region. In this paper, a slope climbing dune in the floodplain of the middle and lower reaches of Yarlung Zangbo River, we analyzed the grain size characteristics and and spatial differentiation of surface sediments on four overlapping crescent-shaped dunes of a climbing dune, named Fozhang dune in the lower Yarlung Zangbo. The results of particle size analysis show that frequency distribution curves of the surface sediment of Fozhang dune, dominated by poorly sorted medium sand, is extremely positive biased and narrowly peaked. In the case of four individual superimposed crescent-shaped dune, the coarsest and best sorted particle fraction emerges at the top of the slope. On the whole, the surface sediment of Fozhang dune has become finer and better sorted towards the crest, which results from the combined sorting of wind and gravity. The grain size characteristics of Fozhang dune is comparable to other aeolian dunes of similar genesis. However, Sahu criterion indicates that the Fozhang dune is fluvial-originated. Maybe Sahu criterion cannot identify aeolian sand of very proximal material source from river floodplain. The comparison of grain size characteristics of sand samples with those of floodplain suggests that Fozhang dune is mainly provided with sand source by materials carried by rivers.