Abstract: Associated stratigraphic water in an oil and gas field contains a variety of information on oil and gas geology and may provide important evidence for evaluation of trap conditions and the distribution patterns of hydrocarbon accumulations. It is closely associated with oil and gas reservoirs and affected by many geological factors, such as hydrocarbon formation and storage conditions, post-storage conditions, geological and geochemical characteristics related to hydrocarbon migration and accumulation processes and the later trapping and preservation conditions. The total mineralization or salinity of the associated stratigraphic water in the middle-deep layers of the gas fields under high temperature and overpressure in the Ledong District of the Yinggehai Basin is abnormally high (60 000 mg/L-80 000 mg/L). It is a kind of weak acid-weak alkaline brine rich in CaCl₂ with a pH of 6-8. Based upon the geological and geochemical characteristics of the associated stratigraphic water, we discussed in this paper the genetic relationship between the stratigraphic water and the migration and accumulation of gas.