Soil erodibility is the intrinsic factor which has effect on water erosion on slope and is related to soil texture , soil organic matter , and other soil properties. Sediment particle is analyzed by using plot data from rainfall simulation experiments.Results show that ( 1)during rainfall, particle composition of sediment changes with time . Sand content increases, silt content keeps constant , and clay content decreases. ( 2) Rainfall intensity is the important factor to the particle composition of sediment . With rain intensity increasing , sand content increases and slit and clay contents are reduced. ( 3)The effect of slope gradient on sedi- ment is complicated . When slope becomes steeper , sand content increases first and then decreases, whereas silt and clay contents decrease first and then increase . When slope gradient is 20 ° , sand content reaches the maximum and slit and clay contents, the minimum.