Abstract: The earth surface sediment transport is composed of two parts:the transport of non-soluble debris and that of dissolved solids,which are the results of mechanical and chemical denudations.Accordingly,the following index is proposed to describe the composition of total sediment transfer:I=D_c/D_t=D_c/(D_c+D_m) where D_c and D_m are surface sediment transfer due to chemical and mechanical denudations,respectively,D_t is total surface sediment transfer.This index is found to be closely related to zonal natural factors such as precipitation,temperature and vegetation.The D_c/D_t value increases with mean annual precipitation and runoff,and decreases with drainage basin dryness index.In the monsoon influenced eastern China,from south to north,this index decreases rapidly,reaching a minimum,and then increases.This areal variation may be explained by the relation between the chemical and mechanical denudations in different natural zones,which in its turn is controlled by the specific combination of climate and vegetation in each zone.The forest cover in the eastern China is found to vary latitudinally in the same way as the index D_c/D_t,indicating that vegetation is an important factor controlling the relation between chemical and mechanical denudations.