The sliding face and the upside rock body are composed by different mechanical property materials. The upside rock body is elastic medium (called medium 1); the sliding belt medium is strain-softening medium (called medium 2). Damage softening and water softening exist to the medium 2. The shear stress-strain relationship is described by the Weibull’s distribution law. In this way

a swallow-tailed catastrophe model of landslide system is established. Through the analysis

it is discovered that the slope steadily have enormous relatedness with the stiffness ratio λ of medium 1 and medium 2 and the water content of sliding surface medium. Along with the increase of water content the value of ξ0 decreases when slope starts to slide

and the value of sudden jump ξ* decreases when skip occurs. At the same time

the critical value x* increases

the skip quantity △x decreases

and λ increases. It is found that the increase of λ or water content has the same distortion rule to slope. That’s why under the condition of rainfall

the landslide becomes unstable easily.