Abstract: Slope instability under rainfall has a series of omens. In this paper, it is proved that rainfall infiltration play a very important rule in the process of the slope failure by the model test method. The mechanism of slope failure caused by rainfall infiltration is explained with numerical simulation method. Several monitoring methods were applied to the model test in this paper. In the model test, variation of soil water content is available by TDR-3 Sensors, and erosion situation of slope body can be observed before its unsteadiness, which show that the nature causes of the landslide are the variation of Soil water content and the water softening. To conclude time-strain relations as well as the evolution of slope-mass slide displacement through monitoring the slope strain variation with FBG Sensors. Then the potential damage position of week structural plane can be located. In addition, dial indicators were used to monitor the displacement of the slope. The slope failure is divided into three stages: initialization phase, creeping and sliding stage, acceleration phase and describe the characteristics of each stages. In the end, the forecast methods of slope failure are put forward with the histogram of the landslide speed.