Abstract: A wide difference of salinity of over 700 times exists in oil field water in eastern China,ranging from fresh to brackish to salty,with apparent ionic differential purification and high concentration of Cl^- and Na⁺. SO₄⁼ increases with increasing salinity,while HCO₃ increases with decreasing salinity. Classified according to salinity, main compounds,character of ionic association and other components,the oil field water in Songliao basin is of the fresh Cl·HCO₃-Na type,in Jiyang depression of the brackish Cl-Na type and in Jianghan basin of the salty Cl·SO₄-Na type.