Abstract: SZ36-A oilfield is a big oilfield with hundred-million tons in Bohai offshore field. The mainly oil-bearing is concentrate on Paleogene Ed2 formation. Through integrating theory with practice, geophysical with geological, reservoir characteristics with sedimentary facies and exploration with development, the rules of reservoir microscopic characteristics and its main controlling factors have been analyzed in this paper. The favorable reservoirs are mainly distributed in lake delta front. At the same time, diagenesis has been analyzed, which calculates the relative of clay minerals component temperature and pressure fields, liquid's filling and other important effects on reservoir characteristics. The sets of reservoir extension have bigger thickness, which belongs to high porosity and high permeability favorable reservoirs.