Abstract: Based on the data of drilling,coring,microscopic analysis and XRD,the diagenetic sequence and secondary pore development of the Paleogene sandstone reservoirs in the Dongying Sag were stu-died.It was considered that the Paleogene sandstone reservoirs were buried more than 3 000 m and were at the stage of late diagenesis A,B and C.The influence factors of reservoir pores mainly included primary deposition,diagenesis,bioturbation and structural condition,in which sediments characters,temperature,pressure and fluid could affect the diagenesis strength to some extent.Three secondary pores zones were developed in Dongying sag as a result of actions of acid formation liquid caused by the organic matter maturation,clay minerals transformation and thermochemical redox reactions of hydrocarbon and sulfate minerals in the Paleogene sandstones in different tectonic block from late diagenesis A stage to late diagenesis C stage.