Grain- size distribution is the information carrier of depositional environment for sediments. The evolution processes from river- bed sand- wave to aeolian dune is in complicated and special sedimentary dynamic mechanism. In order to discuss fluvial——aeolian dune depositional environment features, modern sedimentary of low- beach at the head of Tianxing Central- bar in Wuhan section of Yangtze River was investigated in this paper. Methods:68 sediment samples were taken in different depositional environment, and grain- size distributions are acquired by corresponding experiment. Based on this data set, 4 grain- size end- members, EM1, EM2, EM3 and EM4, are optimized and extracted from each grain- size distribution using end- member analysis. Similarities and differences of grain- size end- members in different depositional environments are discussed further. Results: The results show that percentage of EM1 and EM3 components in grain- size distribution are well linear positive and negative correlation with grain- size median respectively. Fluvial sediments are mainly transported by jumping subpopulation which is composed of EM1, EM2 and EM3 components; EM4 component suggests the rolling subpopulation and its percentage is about 5%~10%; suspending subpopulation is few. Aeolian sand- ripple sediments include 2 jumping subpopulations; EM2 is dominant end- member, EM1 and EM3 are secondary components, few EM4 components. In the leeward slope of the dune, sediments slump by grain- flow downslope; EM2 is primary, and EM1 and EM3 is secondary components; percentage of EM4 components is about 5%. Some dune wave- troughs are not been transformed by wind, and not covered by aeolian sand- ripples. These sediments recorded the depositional environment characteristics of fluvial and small stagnant water simultaneously; corresponding fluvial rolling subpopulation, percentage of EM4 components is about 7%~15%; percentage of suspending subpopulations may be up to 20%. Conclusions: Grain- size end- member extracted in this paper offers reference information for researching sedimentary environments and evolutionary processes of small- scale fluvial—aeolian dune in river channel with weak wind.