Poor understanding on sedimentary system of Dongying Formation in Jiyang depression，the stratigraphy deposited at the end of basin faulting and depressing，has caused uncertainty in its reservoir distribution，reservoir type and hydrocarbon accumulation rule，which restricts the exploration of Dongying Formation. Based on the principle and methods of sedimentology，combining with data of comprehensive mud logging，logging and seismic data，it is determined that a large braided river delta sedimentary system formed crossing the east depression under the monocline structural background during the sedimentary period of Dongying Formation in Jiyang depression through analyzing geologic structure features and palaeogeography. A braided delta developed mainly at the third period of Dongying Formation. The lacustrine basin began to regress and the sedimentary area became smaller and smaller at the second period of Dongying Formation，in which shallow beach lacustrine facies formed in the east combining with depositions of small proximal fans and subsea aprons，and fluvial facies deposited mainly in the east. The lake regressed continuously at the last period of Dongying Formation，and fluvial facies and shallow beach facies developed widely. In the plane，sedimentary patterns changed from braided-delta plain subfacies and delta front sub-facies in Dongying sag in the south to pro-delta sub-facies in Zhanhua-Tanhai area in the north. Slump turbidite fans developed at the front of delta. The sedimentary model establishment of Dongying Formation not only perfects the Jiyang depression’s sedimentary evolutionary sequence of Cenozoic era and guides the direction of reservoir prediction in Dongying Formation，but also lay a foundation for the study on reservoir forming condition of Dongying Formation.