Abstract: The Biyang Sag in the Nanxiang Basin is very favorable for hydrocarbon accumulation.Formation and development of the sag are controlled by 2 deep-large faults in the south.Superior oil generation conditions,abundant sediment resources,development of sand body,good reservoir conditions,good source-reservoir-cap rock assemblage and multiple trap model configurations are favorable for accumulation.Subtle oil and gas reservoirs can be divided into 5 major types and 19 subtypes.In plane,reservoirs locate in circles,controlled by source sag.Vertically,they are influenced by temperature and pressure.Displacement sections of large boundary faults are favorable for large-scale sandstone pinch out reservoir.Inherited sedimentary-tectonic slopes are the targets for large-scale hydrocarbon migration.Oil and gas us-ually accumulate in nose-like uplifts.Deep sags are favorable to find low system trace fans,dolomite oil and gas reservoirs and deep-basin oil and gas reservoirs.Controlled by geometrical patterns,rollover faults can be found at the 2 ends of boundary fault.