Abstract: Aiming at high temperature and high salinity reservoir, clay is optimized to plug large pore paths. Particle size distribution of stabilizing Na-bentonite is characterized by laser particle analyzer and dispersity by the method of bleeding index. The results show that stabilizing Na-bentonite has good behavior of dispersity. However, it is nonuniform in size, and the adaptive permeability is in a range from 3 to 20μm², which is proved by injectivity test. Plugging ability and plugging mechanism of clay plugging system are studied, including clay dispersion system, curing system of clay and super-fine cement, flocculation system of clay-AM-AMPS and clay-phenolicresin gel. Curing system of stabilizing Na-bentonite and super-fine cement was successfully applied to two wells in Gudao oilfield in 2009 and achieved good effects.