In the upper Yangtze block, the Mesoproterozoic most widely outcropped in the Huili—Dongchuan area. Being divided by a east—west direction extentional fault, Caiziyuan—Matang fault, the Huili Group is on the north side, and Tangdan Group, Dongchuan Group are on the south side, and in the fault belt is the 5th Member of the Tong’an Formation. All of them are epimetamorphic sedimentary rocks with interbeds of volcanic rocks.Based on synthetic research in sedimentology, volcanic petrology and isotopic chronology, writers finger out that a east—west directional rift basin formed in Mesoproterozoic(1800～1650Ma), in which acumulated the Hekou Group, composed of metalkaline spilitic—keratophyre and pyroclastic sedimentary rock formation. The time of the Dongchuan Group is Calymmian, the zircons from tuff in the Heishan Formation of which give out a SHRIMP UPb age of 1503±17Ma, formed in extensional environment in passive continental margin. The time of the Huili Group is about Stenian, has volcanic assemblage characteristics of continental margin—islandarc. The 5th Member of the Tong’an Formation is rift—deep sea sedimentation. So the Huili Group and the Dongchuan Group formed in different time and different environment, were individual before Neoproterozoic; the Caiziyuan—Matang fault could be considered as their boundary to keep their independence.