Abstract: Paleodictyon was found in turbidite deposit in the upper of the 4th member（E_s4） of Shahejie Formation in Niuzhuang sag and its morphological feature is similar with that in deep marine.Moreover,dinosterane was still discovered in the host lithology of Paleodictyon.Dinosterane is a sign of marine transgression.These indicate that marine transgression happened in Niuzhuang sag or sedimentation of this sag is related with marine.This cognition not only provides a firm foundation for settlement of the question "whether marine transgression happened or not in Paleogene of Bohai Bay Basin",which has been debated for more than 20 years,but also guides the exploration activity.