Abstract: There are several oil and gas pools found in different zones (the slope zone, fault zone, etc.) in Maichen Sag, Beibuwan basin. In order to identify the stages and features of hydrocarbon accumulation in different zones, the feature of reservoir fluid inclusions, the accumulation stages and process have been studied by using fluid inclusion technology. The research results show that there are at least three stages of hydrocarbon charging and accumulation in Maichen Sag, which are the early Miocene, Middle Miocene and the late Miocene. Three-stage hydrocarbon accumulation has different features. During Stage I, oil and gas migrated and accumulated along faults as "pipe flow". During Stage Ⅱ, oil and gas migrated and accumulated along the connected fractures as "network flow". During Stage Ⅲ, oil and gas migrated and accumulated along the limited connected pores. Then the accumulation patterns of different zones have been established by examples. The slope zone is an accumulation pattern with lateral migration as the major and vertical migration as the minor. The deep depression zone and the fault zone are characterized by vertical migration as the major and lateral migration as the minor.