To evaluate the stability of gravitational erosion for small watershed on the Loess Plateau,the conceptual model of Wangmaogou watershed is explored with the aid of the finite difference software,Flac3D,and the numerical simulations for stress field,displacement field and plastic yielded zone are made as thewatershed system is in balance.The reliability is analyzed for the failure probability of gravitational erosion,combined with Rosenblueth moment estimation method.Results show that.The shear plastic zone is greatly located in the most area of slope and gully slope,and the tension plastic zone is mainly located on top andslope of barren hill.The gravitational erosion of watershed is in unaccepted risk level and effective engineering measures should be taken to improve its stability.Rosenblueth moment estimation method can effectivelycombine the conventional safety factor with probability distribution,which may offer a better approach to thebuilding of evaluation index system for watershed stability and gravitational erosion reliability.