To clarify the indicative significance of fluid inclusions and hydrocarbons in Ordovician carbonate reservoirs in the South of Yan’an，southeast of Ordos，a comprehensive analysis of the petrology，homogenization temperature，salinity and compositional characteristics of fluid inclusions was carried out. Combined with the burial history and thermal evolution of the study area，the hydrocarbon charging history of the reservoir was discussed. According to the phase characteristics，components and hydrocarbon occurrence distribution of fluid inclusions at room temperature，the fluid inclusions of carbonate reservoirs in the study area can be divided into five categories：aqueous inclusions，gaseous hydrocarbon inclusions，liquid hydrocarbon inclusions，bituminous inclusions，hydrocarbon-bearing aqueous two-phrase fluid inclusions，and there are still local residual free liquid hydrocarbons and migrabitumen which do not form fluid inclusions. The results show that the fluid inclusions and hydrocarbons in the study area are mainly distributed in authigenic minerals such as calcite and quartz that fill the pores，the cavities and the fractures of the reservoir. The homogenization temperature gradually increases with the increasing salinity，and the captured fluid inclusions are mainly the products of the source rocks in the high maturity stage. The Ordovician carbonate reservoirs were charged in two stages，the end of the middle Jurassic and the late of the early Cretaceous，and the latter is the main stage.