Abstract: The tight oil reservoir of the Middle Permian Lucaogou formation in Jimusaer sag is of good hydrocarbon potential. Its enrichment mechanism is greatly different from that of conventional oil?gas reservoirs. This paper calculated the fluid pressure of this formation,established the abnormal high pressure distribution system of it, and combined with the geologic conditions, geochemical analysis and formation testing of key wells, it discussed the relationship between the abnormal high pressure and tight oil enrichment. The results show that the Lucaogou reservoir is of typical source?reservoir structure, and the tight oil generated from high?quality source rocks in low mature?mature stage is characteristic with both source and reservoir within the source rocks, and migrates in short distance between source rocks,which is the main reason for forming the abnormal high pressure. Such abnormal high pressure is widespread in the source rocks and the reservoirs, with lateral stability and connectivity, showing a certain stratabound characteristic; with longitudinal differences in organic matter abundance and hydrocarbon?generated ability in different strata, resulting in uneven distribution of the abnormal high pressure, indicating that there exists distinct remained fluid pressure of interlayers. Such a remained fluid pressure could be the main force for the tight oil vertical migration, and the distribution belt of big difference of the remained fluid pressure of interlayers might be the favorable area for tigh oil enrichment