Abstract: In order to study the rainfall infiltration characteristics of double-layered soil slope covered by a highly permeable stratum， the soil column and slope model of homogeneous silt and sand-soil were established respectively， and the governing equations according to the matric suction and water content were used to analyze the effect of permeability， ground water level and slope angle on the formation of saturated zone. The results showed that the formation of saturated zone in sand-soil column is caused by the water accumulation under the sand layer due to the permeability difference， and the dramatically decrease of seepage velocity in the surface of the silt layer. The saturated zone is initially formed in the interface of the soil layer in the sand-soil slope and develops along the interface till to the upper boundary of the slope. In the meanwhile， it gradually develops into the soil layers and up to the interface of layers in the longitudinal direction. The extension length along the soil interface gradually increases with the increase of the groundwater table， but when the groundwater table is 2m and 1m， the extension of the saturated zone is reduced with the increases slope angle. The initial saturation degree is affected by groundwater table and slope angle.

Key words: rainfall infiltration, unsaturated soil, underground water, slope angle, layered soil slope