Physical fractionation and chemical-analysis were used to assess the composition and distribution of organic C,N and P in different sizes of water-stable aggregates of red soil under different land uses.The change mechanism of soil nutrients in transformation between forestry land and agricultural land was analyzed.The27soil samples were collected for testing and were divided into three groups:natural forest land,agricultural land and afforested land.The results showed:that forest clearing and continuous cultivation for upland led to significant depletion of total soil organic C and N,and led to transform of organic P into inorganic P in surface soil.The decline of organic C was more than that of N in the soil.Organic C and total N content in natural forest land were3.19and1.15times more than those in agricultural land respectively.The proportions of particulate organic C to total C in natural forest land,agricultural land and afforested land were65%,11%and47%,respectively.The change of land use has great influence on the contents of particulate organic C and organic P in the>1mm aggregates.