In 1950~1960s, Liu Tungsheng organized field and laboratory investigations on ten loess transects(six meridional and four transverse directions)across the Chinese Loess Plateau, confirmed the southeastward fining pattern of loess grain size in the Loess Plateau, and identified zones of sandy loess, loess and clayey loess from northwest to southeast. Since then, loess grain size has become a basic palaeoclimatic proxy. However, the palaeoclimatic significance of loess grain size remains debated. In this study, 57 loess sections(above soil unit S2)in the Loess Plateau were sampled and analyzed in the main body of the Chinese Loess Plateau. The grain-size records from the Loess Plateau clearly display an overall southward decrease in particle size in the case of both loess and soil horizons. The grain-size contour maps were constructed for the Last Glacial Maximum and the last interglacial. All the grain-size isolines show a near north-south gradient for both the Last Glacial Maximum and the last interglacial. By combining the glacial-interglacial changes in the extent of deserts in Northern China and corresponding loess grain size variations, we suggest that the source-to-sink distance plays a primary role in the downwind loess grain size variations, and the effect of the winter monsoon intensity is secondary. In this context, a model of median grain size versus the minimum source-to-sink distance was developed, on the basis of loess grain size data from the Hongde-Yangling transect. According to this model, the dust deposits show a rapid differentiation in grain size within a transport distance of 400km, in which the Chinese Loess Plateau is right located. From 400km to 2000km, the dust deposits show a gradual differentiation in grain size, as represented by the Neogene red clay in the Loess Plateau. After transport of over 2000km, the grain size of the eolian grains is in equilibrium with the transporting winds and becomes essentially constant, as exampled by the eolian deposition in the deep sea. The grain size-distance model, based on loess deposits transported by low-level winds, predicts median grain sizes of 1~3μm for the dust deposits transported over 2000km, similar to those(3~4μm)of both the high-level transported modern dust collected over the North Pacific Ocean and the eolian dust preserved in deep-sea sediments. This may reveal an inherent dynamic characteristic of wind regime on Earth, which requires investigation in future studies.