Sediments were sampled on the windward slope of a typical barchanoid compound mega-dune with a height of close to 420m in southeastern Badain Jaran Desert for grain-size distribution analysis. Study of grain composition and the reasons for variation of mega-dune, activity and changes in power of mega-dune. The analysis results indicate that the surface layer sediment size is higher than that of sub-surface layer on the windward slope of the mega-dune. The surface sediments contain almost the same fraction of medium and fine sands, being 47.48% and 39.43% respectively. However, the sub-surface sediments contain significantly higher fraction of fine sand. The content of medium and fine sand is 40.96% and 54.01%respectively. The fraction of very fine sand very coarse sand and coarse sand in both surface and sub-surface sediments is insignificant, and clay are absent. Wind erosion is responsible for the difference in grain size between the two layers. In general, grain on the crestal zone of the mega-dune is finer and better sorted than that at toe of wind-ward slope. The frequency distribution curve becomes more negatively skewed, but there is no typically changed on kurtosis. The reason of thinning from the lower to the top of the Mega-dune are terrain increase and slope increases.Coarser and more poorly sorted sediments appear on the middle to upper section of wind-ward slope of the mega-dune due to local topographical relief and air current. Mega-dune coarse granularity of the surface shows that, Material of mega-dune being in the event of mobile,is the activities mega-dune. Comparing Wind in the other dune of China, the wind is maximum in Badain Jaran Desert. that is the one reason of coarse granularity. That also must be the dynamic conditions to the formation of greatest mega-dune own height difference.