Abstract: The relationship between the fluid inclusions and hydrocarbon accumulation in the eighth member of the Lower Shihezi Formation in northwestern Ordos Basin is based on diagenetic sequences,homogenization temperatures,freezing point temperatures,salinity and density of the hydrocarbon inclusions and hydrocarbon-bearing salt water inclusions,in integration with structural features,burial history,vitrinite reflectance,apatite fission-track dating.Four phases of hydrocarbon accumulation are identified for the study area,including:(1) 219-209 Ma(middle Late Triassic);(2) 191-183 Ma(middle Early Jurassic);(3) 145-130 Ma(early-middle Early Cretaceous),and(4) 122-115 Ma(late Early Cretaceous).