Abstract: Delta facies oilfields in Paleogene Dongying Formation of Bohai Bay are the main oil-bearing series. In this paper, the geological characteristics of delta facies oilfields of main Dongying Formation in Bohai Bay have been studied, focus mainly on structure, stratigraphy, sedimentation, fluid and reservoir characteristics. The reservoir description on the distribution characteristics of fluvial delta facies and braided river delta sandstone facies reservoirs have been conducted. Based on the study results, the fluid distribution characteristics and reservoir modes of such oilfields have been discussed. It is believed through study that most of the delta facies oilfields are large scale reservoirs, and the reservoir lithology is mainly unconsolidated sandstone, with high porosity and high permeability. The reservoirs are characterized by steady distribution, relative large thickness and good physical properties. The oils are mainly heavy oil, and secondly medium and low viscosity oils.