Abstract: The quantitative characterization of diagenesis and diagenetic reservoir facies has been made for three types of diagenesis in the low permeability reservoirs in the 3rd and 4th members of the Quantou Formation in the Xinli Oil Field, Jilin by using the techniques of quantitative statistics of cast thin-section, cathodoluminescene and SEM. The intensity of each type of diagenesis is evaluated.The types of the diagenetic reservoir facies are summarized, on the basis of lithofacies, diagenesis types and intensity, reservoir properties, including:strongly corroded secondary porosity type (Facies A), moderately compacted and weakly to moderately cemented mixed porosity type (Facies B), strongly compacted and weakly to moderately cemented mixed porosity type (Facies C), and strongly carbonate-cemented type (Facies D). Facies A is most favourable for hydrocarbon accumulation, followed by Facies B and C. Facies D is worst. The examination of the characteristics and evolution of the above-mentioned diagenetic reservoir facies shows that the secondary pores generated by acidic formation water formed during the late diagenetic stage may be considered as the key factors for the improvement of the physical properties of the reservoirs in the study area.