Abstract: On the basis of the features of sedimentary facies,material source,biological assemblages,geochemical facies,the abundance and types of organisms,hydrocarbon potential,etc.,the paper makes a comprehensive study on the organic facies of major oil-gas source rocks in the Permian system of the Lower Yangtze Region.Meanwhile the concept of organic facies is proposed.It is suggested that the organic facies can be clarified into subfa-cies of highly oil-prone phase(A),oil-prone phase(B₁),gas-prone phase by oil cracking(B₂),oil-gas mixing phase(B-C),oil/gas barren phase(D)respectively in accordance with the classification of organic facies and their indices.