In order to explore the formation conditions of transient saturated areas of a coarse-grained soil embankment slope with rainfall infiltration, and to investigate the effects of rainfall infiltration parameters on the development of the transient saturated areas, we designed various numerical calculation schemes using field and laboratory data and actual meteorological data, and conducted numerical simulation of the rainfall infiltration process of the coarse-grained soil embankment slope under the influence of rainfall infiltration parameters based on the theory of rainfall infiltration. The results show that the rainfall infiltration direction and formation of transient saturated areas were determined by the ratio of rainfall intensity(q)to saturated permeability coefficient(k_sat). When q/k_sat ≥1. 5, transient saturated areas with a certain depth formed at the embankment slope surface and slope toe. The formation of the transient saturated areas increased the possibility of embankment failure. The rainfall infiltration only caused the water level under the embankment slope surface to increase significantly, but had limited influence on the groundwater level below the central road. The expanding speed of the transient saturated areas was mainly determined by q and k_sat, while the formation time and expansion area of the transient saturated areas were influenced by q, rainfall duration, and saturated water content.