Abstract: This is a study of the correlation of different salinity with the viscosity of polyacrylamide solution of different degree of hydrolysis.The mechanism of sensibility to salinity for partially hydrolyzed polyacrymide is explained by the relationship between the dissociation and equilibrium of carboxylic sodium group existing in the polymer solution in water with the viscosity of polymer solution. In polymer flooding,partially hydrolyzed polyacrylamide fluid slug prepared with water of high salinity is first injected,followed by fresh water.It has the following advantages:good pumpability,reduced shearing degradation and the capability of bringing the residual resistance of PHPAM into full play in controlling water mobility.