On the basis of seismic, logging, well logging and gravity data, through the full 3D fine structure interpretation and comprehensive analysis of the residual gravity anomaly field, it is shown that South Turgay Basin consists of a double tectonic basement with relatively rolling topography and well-developing deep faults. All of 4 NW-SE trending sags distributing from west to east are characteristic of down-faulting at the eastern boundary and overlapping at the western boundary. The depth of the basement generally changes from 1km to 5km, characterized by being deep in south and shallow in north. By action of north-west fault system, most of basal local structures are in northwestward distribution. By the analysis results of conditions of hydrocarbon accumulation in buried-hills, including lithology, reservoir property, source-reservoir-cap assemblage and preservation, three models of basal hydrocarbon accumulation are established, which break through the knowledge that only the weathering crust in buried-hill is oil-bearing in this area.