Abstract: On the basis of analyzing lab experimental methods of water blocking damage,a simple and effective lab method of qualitatively studying effect of water saturation on water blocking damage is presented in this paper,which is called reversed action method.The process is to put cores to core holder and exert pressure on exit end surface so as to result in water blocking damage by the corresponding reversed liquid into the cores.This is used to further develop experimental methods of water blocking,and supplies theoretical direction for lightening or eliminating water blocking damage in the low- permeability sandstone reservoirs.