Abstract: Hydrocarbon in the West Sag of Tanhai area,the Liaohe Basin was mainly derived from the source rocks of the Es³ and Es¹⁺² Member.By integrating the methods of well core analyzing and logging calibrating,the effective thickness of source rocks and their distribution were determined.Faults,connec-ting sandstones and unconformities were the three main pathways of petroleum migration in the study area.They singly,or combined with others,controlled the migration and accumulation of oil and gas around main hydrocarbon-bearing zones.Moreover,composite trap zones led to the formation of composite hydrocarbon accumulation zones.Hydrocarbon pool-forming conditions matched with each other,and formed characteristic accumulation models and distribution rules in every composite hydrocarbon accumulation zone.The distribution of oil and gas was clarified for guiding the future petroleum exploration of the area.