The Xinli Oilfield is located at the Xinmiao Village north to the Guo County in Songyuan City, Jilin Province. Based on the comprehensive analyses of the analytic data of thin sections, vitrinite reflectance, scanning electron microscope, xray diffraction of clay minerals of core samples from 25 wells, the diagenesis, diagenetic evolution succession, and the types of the reservoir pore space have been studied. Based on the diagenesis and its proper combination of reservoir pore space, the reservoir rock is divided into 4 types of diagenetic reservoir facies: Facies A, the secondary porosity diagenetic reservoir facies formed by strong dissolution of instable ingredients; Facies B, the mixed porosity diagenetic reservoir facies formed by moderate to weak compaction and cementation; Facies C, the  remaining intergranular porosity diagenetic reservoir facies formed by strong compaction and moderate cementation; Facies D, the  microporosity diagenetic reservoir facies formed by strong carbonate cementation. The characteristics of each diagenetic reservoir facies are described in detail, and the  petrophysical properties of the reservoirs change from good quality to poor quality as follows: Facies A, Facies B, Facies C and Facies D. Finally the reservoir pore space evolution of the Quantou Formation has been discussed. A great deal of secondary porosity was generated in the age A  of middle diagenetic stage, which provides the scientific proofs to forecast the relatively favorable diagenetic reservoir facies belts in extremely low permeable reservoirs in the Quantou Formation of this area and a solid geology foundation for improving the exploitation effects of extremely low permeable oilfields is established.