Abstract: The general behavior of sludge from 8 dam-sites is studied, which are located in southern part of China. On the basis of investigation in situ and sampling, it may be classified into two types. One is common with relatively wide distribution, of which the content of SiO2 and Al2O3 is quite low, i.e. < 10%, although the different sludge in color has different major chemical component. The other is special with unusual distribution, where its outcrop has good in correspondence with geological deficiency bodies, such as sandwich, fault zone and others. Furthermore, the content of SiO2 and Al2O3 is relatively high, i.e. < 30%. From these, it is believed that the latter type may produce a relatively obvious influence on seepage stability. Therefore, it is necessary to keep monitoring its tendency.