The formation of water chemical characteristics in the Paleogene System had good response to the sedimentary conditions and its evolution in Dongying sag. The type of CaCl₂ formation water with high salinity was representative response of the brine lake of the Paleogene System in Dongying sag. The content of total salinity and chloride ion decreased from the deep depth to the lower, which was good response to the evolution of the Dongying sag from salted basin to freshwater basin. According to the vertica1 characteristics of the underground water formation, four hydrological environments can be classified: stronger formation water frequency alternation belt(0-1.1km), feeble formation water frequency alternation belt(1.1-2.0km), formation water alternate blocking belt (2.0-2.5km) and formation water alternate tardy belt (>2.5km). In every belt the total salinity, ions and ion composition ratio had different responses, and the belts corresponded to the distribution of formation pressure. The formation water chemical field experienced deposition and leaching in early time and burial in later time. In the period of Dongying Movement the formation water chemical field was active, and salted water from the Member 4 of Shahejie Formation migrated to the lower, and in the course the faults played important roles, which demonstrated the representative characteristics of faulted basin.