Abstract: There exist soils with diluvial or pluvial genesis and bad engineering properties on the river slope in Three-Gorge Reservoir reg ion. I t is obvious that, the soils are classified as low expansive by the national sta ndard, or medium to high expansive according to the current international e xpan sive potential chart from Williams & Donaldson(1980). By advanced clay test te chnology-XRD, it is disclosed that the expansive clays mainly consist of mixed-layer mineral I/S with middle mixed-layer ratio. And finally, their ha zar d mechanisms are researched and the curing methods are put forwards. Research on the expansive soils is of great significance for the improvement of expansive soils in Three-Gorge Reservoir region.