Longitudinal dunes are widely developed in the northeastern Taklamakan Desert， but the particle size characteristics of sediments have rarely been reported. The sediment grain-size characteristics of a longitudinal dune profile and an overlying secondary dune profile in the northeastern Taklamakan Desert were determined by sieve analysis. The results showed that： （1） The sediment particles of the longitudinal dunes gradually became finer and poorly sorted from the top of the dune to the bottom of the slope on both sides； the same was true for the overlying secondary dunes. （2） The frequency distribution curves of the longitudinal dunes sediments was mainly bimodal. （3） The average sediment size in the middle of the windward slope of the longitudinal dune was finer than that in the middle and lower parts； the sediment particles in the bottom of the windward slope of the overlying dunes is coarser than that in the middle of the windward slope. It is concluded that the particle size distribution of the longitudinal dunes in this area is consistent with the "coarser ridge type" proposed by previous authors. The bimodal distribution of sediment samples is significantly influenced by the source and wind selection. The coarsening of the bottom of the windward slope on the overlying dune profile may be due to the enrichment of coarse particles that cannot be carried away. Local changes in the morphology of the overlying secondary dunes of the longitudinal dunes affect the wind-sand flow， which leads to local changes in the mean particle size and sorting coefficient. There is a secondary transport process of wind and sand flow on the windward side of the sand monopoly.