Reservoir rocks of early Cretaceous Denglouku and Quantou Formation in the Yaoyingtai area of southern Songliao Basin are mainly composed of feldspathic litharenite and litharenite arkoses, with low compositional and textural maturity, belonging to ultra low porosity and permeability reservoir. The Denglouku Formation with high porosity and permeability distributes in the Y81 well field. The study shows that the reservoir rocks is in the A period and B period of late diagenesis. Diagenesis mainly affects the porosity and permeability of reservoir. Compaction, cementation, replacement and secondary overgrowth of the reservoir rocks contribute to the rapid reduction of primary porosity and permeability, which are the main reasons resulting in the poor physical properties; but dissolution is the main factor for formation of secondary porosity, which improves the physical properties of the reservoir sandstones.