A series of experiments of slope rainfall erosion were done in laboratory for steep loess slope with slope angle of 70° under a rainfall intensity of 2.7 mm/min. According to the characteristics of slope erosion

the evolution of rainfall erosion process is generally concluded as splash and sheet erosion in earlier phase

rill erosion in middle phase

and finally evolved into gully erosion and collapse in later phase. It was found that the degree of erosion at the slope top is stronger than other positions during the experiment; after a through gully formed on the slope surface

the water flow then began to scour soil inside the gully; with rainfall lasting

the strength of the soil around the gully obviously decreased; consequently collapse took place at the slope top and eventually caused wholly demolition of the slope. Based on the experiment

simulating the slope erosion process with PFC3D with fluid-soil coupling method

observing the large deformation of particles

simultaneously the microcosmic parameters such as particle motion trace

porosity and water flow rate in fluid cells are obtained; from their quantitative change process

the distribution of degree of erosion and erosion intensity of water flow in slope is got; it indicated that the degree of erosion and the erosion intensity of water flow at slope top are strongest and both reduced as the height decrease

which is consistent with the indoor model experiment.