Abstract: The reservoirs in the lower unit of the third member of Eocene Shahejie Formation(Es₃³)in Gaoshangpu oil field mainly consist of feldspathic litharenites and lithic arkoses sandstones with the characteristics of low compositional maturity,low textural maturity and rapidly proximal deposit.Important diagenetic processes that have affected the sandstones include mechanical and chemical compaction,cementation,dissolution,precipitation of authigenic minerals,replacement,and cataclasis.Generally,early grain-coating chlorite and dissolution associated with organic acids and/or thermal fluids,as well as cataclasis,are constructive diagenesis for reservoir quality,whereas compaction is the major factors that destroy the porosity rapidly.In addition,carbonate cements and replacements,quartz cements and anthigenic clay minerals are the destructive diagenesis for the reservoir quality.This study indicated that the Es₃³ sandstones are present in the middle diagenetic stage.The space of the reservoirs is composed of the multiple-genetic pores(primary and secondary)that formed from different stages.The reservoir quality with middle-low porosity and low permeability are decrease with depths.A well correlation between porosity and permeability suggest that the sandstones are pore-type reservoirs.The shallow burial(underwater)distributary channel sandbodies would be the most favorable targets for oil and gas exploration in the future.