Abstract: Based on massive data from new well drilling tests, acoustic logging and fluid inclusion analysis, the deep abnormal pressure in Huanxian-Pengyang area and its surroundings are studied to find out the dynamic mechanism of hydrocarbon migration and accumulation of Chang 8 Member in the southwest margin of Ordos Basin. The results show that there is a certain residual pressure difference between the bottom of Chang 7 and the top of Chang 8 members. The plane distribution characteristics of pressure show a gradually decreasing from the center to depression margin, which are consistent with the trend of whole basin fluid pressure. The abnormal high pressure from hydrocarbon generation of source rocks in Chang 7 Member can cause the hydrocarbon to migrate downward on a large scale and charge into Chang 8 reservoir. The restored paleopressure of fluid inclusion by simulation shows that the crude oil still remains a certain abnormal high pressure after charging into Chang 8 reservoir. Compared with the interior of basin, despite the low residual pressure difference between source and reservoir on the whole, it is still the main hydrocarbon accumulation dynamic mechanism of Chang 8 Member in the southwest margin. It is expected that the study can help further understand the accumulation mechanism and distribution rule of low permeability tight oil in the basin margin, and provide reference for expanding exploration fields.