By using finite element method and establishing a generalized model for the classical slope-gully system of Uuandigou watershed

it is found that with gradual rise of dam land

the stability of the slope-gully system is enhanced and the slumping amount is reduced

which separately satisfies binomial and linear rules.Through calculating and simulating by software

the erosion amounts and percentages of gravitational erosion on mound and gully slopes are obtained.For gravitational erosion of the slope-gully system，with dam land rising gradually

ratio of the volume to weight of slumping soil on mound slope or gully slope is about 1:50.In addition

the volume and weight of slumping soil on mound slope are about 2 percent of the volume and weight of the total slumping soil

respectively

while on gully slope

about 98 percent.Thus

the gravitational erosion on gully slope is the main source of channel sediment. Result from the study can provide important parameters and a scientific foundation for predicting and quantitatively evaluating gravitational erolion in small watershed.