This paper conducted indoor simulation test on rainfall for filled soil slope of LiangZhong Expressway and analyzed the law for sediment and runoff generation under different slopes and different rainfall intensity. Results show that under 0.6mm/min, 0.9mm/min and 1.2mm/min rainfall conditions, the initial runoff time decreases with the change of the slope, when the soil slope is certain, the initial runoff generation time continuously becomes small, and the runoff intensity in the surface of the soil increases with the increase of rainfall intensity. When rainfall intensity is certain, the runoff generation time of the soil becomes smaller with the increase of soil slope, and the runoff intensity of soil surface continuously increases. The critical slope of the soil is about 25°. The rainfall intensity has certain influence on the critical slope of soil erosion, but the real change relation between the two needs to be further studied. Based on the research on water and soil erosion mechanism of the expressway slope, this paper analyzes the causes for water and soil erosion in expressway slope and points out the measures for scientifically protecting the slope of the expressway.