The double ring field tests, Guelph tests and laboratory reconstituted permeability tests were carried out respectively to investigate the permeability behaviors of the untreated and treated expansive rock slopes in the main canal of the Middle Route of the South to North Water Transfer Project. The results of the double ring field tests show that both the permeability coefficient and infiltration depth of the marlite are greater than those of the clay stone, respectively, and that the stable permeability coefficient and infiltration depth obtained in geogrid reinforced field are one-fourth and one-second of those receirved in the treatment field with soil bags, respectively. Geogrid reinforced treatment has been proved to be an effective measure for the expansive rock slope. The results of laboratory reconstituted permeability tests show that the permeability coefficient of remolded marlite samples is greater than that of the reconstituted clay rock when their dry densities are the same with natural water content. The decrease of the permeability coefficient of the marlite is more significant than that of the clay rock with the same increase of the dry density. Moreover, the measured permeability coefficients of marlite and clay rock from the laboratory tests are less than that obtained from the field permeability tests, respectively.