Abstract: The Western depression at the west sub-sag,with three effective source rocks as the upper Aershan formation, the lower Tenggeer formation and the first member of Du- hongmu formation,is the unique hydrocarbon-generating depression in Baiyinchagan sag.Analytical results of fluid potential suggest that the hydrocarbon was migrated along five directions;the faults active at a long period is the verti- cal migration pathway of hydrocarbon;and the unconformi- ties and permeable sand rocks are horizontal migration path- ways.Oil and gas are surrounding the hydrocarbon-genera- ting sag in Baiyinchagan depression.The inherited structural traps are dominated in fault belts,while the lithologic traps are the main type in the depression.The horizontal distribu- tion of hydrocarbon is subject to the directions of fluid poten- tial.and the vertical distribution of hydrocarbon is subject to the source rock-reservoir-caprock assemblage and the li- thology,resulting in a different distribution horizon in differ- ent area.Attention should be paid on the lithological config- uration on both sides of fault in fracture zones.