Abstract: The oil and gas maturity, stages of petroleum migration and accumulation of upper and lower petroleum systems of Gaoyou Sag in Subei Basin are determined based on the data of the occurrence, phase types and fluorescence of organic inclusion and the homogenization temperature of synchronous saltwater inclusion. The oil sources and its characters of the two petroleum systems are discussed and compared by geochemical analysis of organic inclusion compositions. The migration direction and accumulation mechanism of lower petroleum system in SN region are studied according to the biomarkers data of organic inclusion and its results is in accordance with that of the analysis of pyrrolic nitrogen compounds. So that such study provides a kind of more direct microscopic proof and method for hydrocarbon migration and accumlation. The successed case study also indicates that organic inclusion analysis has more wide prospect in the study of migration and accumulation in petroliferous basin.