Abstract: On the basis of displacement-time series of the slope, a nonlinear dynamic model is set up according to Backus generalized linear inversion theory in this paper. Due to the equivalence between autonomous gradient system and catastrophe model, a standard cusp catastrophe model can be obtained through variable substitution. The method is used in analysis of displacement data of Huangci landslide and Wolongsi landslide and in understanding how slopes evolve before sliding. The result shows that the nonlinear dynamic model can make satisfactory prediction results. Is it most important that there is a sudden fall of D, which indicates the occurrence of catastrophe (when D=0).