Abstract: The formation of eluates around dam sites is studied in 4 case records on the basis of their chemical compositions and physico chemical index, etc. The influence on seepage stability is appreciated from macro and micro point of view. It is concluded that the eluates are produced generally by chemical erosion under certain conditions, and the physico chemical behaviour between grains may be deteriorated as the time elapses. However, the macro influence on seepage stability is unlikely to exist as long as this kind of erosion is of chemical one.