Abstract: The Jimsar sag is formed in the late Hercynian period, transformed strongly in Yanshanian period, and shaped in Himalayan period. Today it’s a half graben?like sag with fault in the west and overlap in the east. The Middle Permian Lucaogou formation distributs in the whole sag with the major sedimentary assemblage of saline shallow lake and deep lake facies. High?quality hydrocarbon source rocks are in the Lucaogou formation, and the organic matter type is mainly the mixed organic matter of Type Ⅰ and Type Ⅱ1 during mature stage.Compared with the tight oil in other regions, sweet spots of tight oil in Lucaogou formation have characteristics of thin monolayers and large vertical span with two concentrated sections of them. For sweet spots reservoir, the predominant lithology is dolomitic fine?silty sandstone,the porosity of core in net confining stress averages 10.8%, the permeability of it ranges from 0.001 mD to 0.6 mD, being dominated by dissolved micropores.