Abstract: Keelung Sag is an important oil and gas sag in the southern part of East China Sea shelf basin. The evolutional stages of Cenozoic tectonic in Keelung Sag are divided into faulted period in Paleocene and Eocene, post-rift subsidence period in Oligocene and regional subsidence in Miocene.In order to evaluate its oil and gas resource potential more effectively, it is necessary to study the sedimentary facies for the formation of Paleocene to Miocene. The sedimentary facies characteristics of Keelung Sag can be analyzed by a combination of seismic facies and amplitude attributes.With the epicontinental sea sedimentary background, Keelung Sag accepts shelf sand, delta and slope fan sediments on the west side, in the central depression belt turbidite sand body is often scattered. The shallow Marine mudstone of the Paleocene and Eocene in Keelung Sag is the most favorable hydrocarbon source rock.Different kinds of sand bodies of Paleogene on the west side and in the central depression belt can form favorable reservoir.The thick shallow marine mudstone with wide distribution in Miocene can be a stable regional caprock.