Abstract: The hydrocarbon enrichment rules of Bai 306 block Chang 81 in Baibo oilfield is complex with low producing degree.Through the analytical method of core observation,well logging data,cathode luminescence and casting thin sections,its sedimentary environment and micro facies have been studied.Chang 81 oil formation is delta front sub facies,which can be divided into three sedimentary micro facies as underwater distributary channel,channel flank and interchannels.Based on plane distributing rules of three small layers sedimentary micro facies of Chang 81 oil layer,the controlling functions of sedimentary facies to hydrocarbon enrichment has been studied.The result indicates that: The controlling role of sedimentary micro facies to sandbody,layer physical property and hydrocarbon enrichment is obvious,under water distributary channel is Chang 81 formation's frame micro facies,sand body physical property is good and distribution is regularly arranged,which is the most advantageous oil gas enrichment zone.