Dongpu depression (DP) is situated in southern part of Bohaiwan rift, in which main oil and gas accumulations show deeper burial than in other Cenozoic basins.of eastern China. The basin-fill sequence consists of Lower Tertiary of 4000-6000m in thickness, characterized by fine elastic rock intercalated thin halite and gypsum layers of lake fade:, and Upper Tertiary of 1400-2100m in thickness, characterized by grey-variegated elastic rock of fluvial factes. The deeply buried reservoirs generally belong to Sahejie Formation of Lower Tertiary in DP.Based on statistics of reservoir characteristics and thinsection analysis, secondary reservoirs occur in three zones (SA, SB and SC) from shallow burial to deep one.In case of wenliu area, pore texture and diagenetic features of the reservoirs show:(1)the zone SA-buried in 1800-2800m: more mixed genetic pores in which secondary pores resulted from strong dissolution of early carbonate cements and weak framework feldspar dissolution (FGD); a lot of intergranular pore type and enlarged one; (2) the zone SB-buried in 2800-3600m: rich in secondary pores resulted mainly from dissolution of carbonate cements; a lot enlarged intergranular pore type;(3) the zone SC-buried in 3600-> 5000m: much more pores resulted from destroyed grains than the zone SB, but less porosity and permeability.Combined with methods of scanning electron microscopy, electron probe. stable isotope and hydrocarbon-bearing inclusion analysis. different genesis of the above three zones are known. I. The genesis of SA minily attributes to strong dissolution of caronate cements caused by organic acids (esp. dicarboxylic acid); however, weak dissolution of aluminum-silicate minerals occurs in the zone SA, which may be responsible for the following factors: higher concentration of calcium and magnesium canon in pore fluid, higher content of elastic feldspar in mudstones, and thermal decomposition of carboxylic acid.II. Decarboxylation of organic acid increases in SB zone, which makes the rapid elevation of Pco2 and the transition from externally buffering carbonate system to internally buffering one, therefore the secondary porosity is mainly caused by dissolution of carbonate cements resulted from carbonic acid. Especially, abnormal high fluid pressure develops in the zone, which not oilly preserves initial pores but increases the dissolution ability of acidic fluid.III. Besides preservation of abnormal high fluid pressure to initial pores, carbonate-clay mineral reactions and thermochemical sulfate redox may produce CO2 and H2S to form acidic fluid environments, which may promote the development of secondary porosity in the zone SC.Additionally, coal seams of Carboniferous-Permian Period found at the base of DP may be of important significance to development of dissolution in the deeply buried reservoirs because of CO2 released from coalification.Synthetical analysis shows that the SA and SB are of superior reservoirs for oil and gas, however only gas usually accumulated in the SC. There are favourable conditions in the SB and SC where oil and gas accumulations with high pressure may develop.