Based on the Ecological Features of typical karst area in Chenqibao area, Puding County, Guizhou Province, according to basal knowledge of hydrogeology and engineering geology and agrological theories on soil moisture content, the correlation between physical—chemical characters and water content of the soils 20cm beneath surface layer is studied. The test results show that the soil waterholding capacity depends on grain size composition, void ratio and mineral composition of the soils. When the powder grain content of soil is higher, clay grain of content is less, and the size distribution of the soil grain is asymmetry, the waterholding capacity of soil is higher. And the waterholding capacity of soil is positive correlated to the void ratio and clay mineral content value, such as illite—montmorillonite interbeded mineral, illite and chlorite, while negative correlated to primary mineral content, such as feldspar and carbonate minerals. And quartz has no obvious effect on the waterholding capacity of soil.