Based on the permeability and strength theory of unsaturated soil, this study used two expressway embankments consisting of soil with significantly different permeabilities as examples to investigate the variations in pore water pressure and stability coefficient of the embankments during different rainfalls. The results show: (1) The rainfall infiltrates better in lower parts than upper parts of the embankment formed with high permeability soils; however, it infiltrates almost equably in the surface of embankment formed with less permeability soils. (2) The minimum stability coefficient of the embankment slope with high permeability occurred normally after rainfall about 0.5-3 days during the short and high intense rainfall process, or less intense and longtime rainfall process. And the minimum stability coefficient of embankment with less permeability lag behind rainfall more obvious, normally lagging 7-15 days behind rainfall. (3) When the total rainfall is constant, the minimum stability coefficient of the embankment slope with high permeability decrease as rainfall intensity increase. The embankments with low permeability are influenced by both rainfall intensity and duration.