The hydrogeology condition in karst area is the geological foundation of ecological environment, as well as the foundation of water and soil protection. Therefore, the author had studied on the hydrogeology to the Quaternary overburden in the typical karst area of Guizhou province. Geological sections were dug on the Valley and slope land in the south of Chenqibao village in Puding country. By means of several kinds of test, including insitu and laboratory tests, the physical properties, mineral composition and permeability of soil were measured. Based on the test results, the environmental signification of clay minerals had been analyzed in the surface soil . The results showed that permeability of soil in karst area was effected by the soil structure, grain size composition, mineral composition and plant root. Especially, because of the expansion of the montmorillonite and the late of soil formation age,. the cohesion of soil was weakened, the soil mass is easily eroded, it is baleful to soil and water conservation. The measures using ecological vegetation protect soil and hold water were needed.