Abstract：This paper studied the characteristics of fluid inclusions, based on technical methods of fluid inclusions and a lot of information and previous results obtained in the Tahe Oilfield. The results show that the fluid inclusions can be broadly divided into H2O inclusions, organic matter inclusions, and organic matter-H2O inclusions. The Ordovician reservoir of the Tahe Oilfield experienced five times of thermal fluid activities corresponding to four times of petroleum charging and one time of gas charging; three different salinity values were obtained; fluid density varies in the range of 0.90~1.15 g/cm3. This paper systematically elaborated fluid inclusions in Ordovician carbonate rocks of the?Tahe Oilfield, pointing out the application of fluid inclusions in such aspects as the diagenetic environment, the function of high-temperature hot water, the low temperature multi-cycles, the oil gas maturity and the oil gas charge.