The formation water chemical characteristics in the Paleogene system had good response to the sedimentary conditions and its evolution 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 fresh water basin. High salinity displayed the main characteristics of the saline lakebasin，and dissolution of salt rock，diffusion and migration of formation water，and the communication by faults were main reasons. In the formation water with high salinity，there mainly developed CaCl2 water type，and in the formation water with low salinity，there mainly developed NaHCO3 water type，and the NaHCO3 water type was substituted by the CaCl2 water type with the content of total salinity increased. There were also developed some Na2SO4 and MgCl2 water types with low to high salinity. The study by the analysis on a great deal of measured data related to formation water and oil or gas demonstrated that，The CaCl2typed formation of water in Dongying depression indicated quasiclosed and reductive conditions，in which the oil and gas reservoirs were most widely distributed，and the reservoirs currently found in high salinity(>100 g/L)were mainly associated with formation water in CaCl2type； The NaHCO3typed formation water with low salinity(<10 g/L)suggested opening and strong alternation in water flow，which was unfavorable for oil and gas accumulation，though some secondary oil and gas reservoirs were found in such environment； The NaHCO3typed formation water with high salinity(>30 g/L)suggested a favorable condition comparatively for oil and gas accumulation，in which primary oil and gas reservoirs were found，and its cause of formation was recommended to be connected with the migration of CO2 in high concentration from the mantle along the channels of faults. The Na2SO4typed formation water with high salinity(>30 g/L)was related to gypsumsalt，in its conditions primary oil and gas reservoirs can be formed，and the Na2SO4typed formation water with low salinity suggested oxidative condition that was also unfavorable for oil and gas accumulation. In the saline faulted lakebasin of Dongying Basin，NaHCO3 water type can representative the openly sedimentary conditions with strong alternation of formation water，and Na2SO4 was relative to the distribution of halite and gypsumsalt. High salinity formation water of NaHCO3 type and Na2SO4 type showed the abnormal formation water field. Some oil reservoirs were found in every condition with low salinity although most oil reservoirs formed in the formation water conditions with high salinity，which displayed the representative characteristics of formation water field in the saline faultedbasin and unique relation of formation water chemical field in salted basin with hydrocarbon accumulation. 