Abstract: Based on the measurements of drilling,coring,microscopic and microscanning,the diagenesis and secondary pore development in Paleogene deep formation in Dongying sag are researched.The results indicated that the clastic rock strata buried in deep depth,they came through strong compaction,cementation,complex metasomatism and dissolution,so the primary pores are few.In all of these diagenesises,cementation is the main factor to decreasing stratum porosity and permeability.Abundance outputting of calcite,pyrite,kaolinite and chlorite were well corresponding with secondary pores growth.The dissolution developed sorts of pores.The acid stratum liquid caused by the organic matter maturation,clay minerals transformation and thermo chemistry oxidation deoxidation reactions of hydrocarbon and sulfate minerals developed 2 to 4 secondary pores zones in the deep formation of Dongying sag in Paleogene on different tectonic block from late diagenesis A stage to late diagenesis C stage.