The characteristics of S1k1 reservior in Shun9 well block of Tazhong were investigated based on the data from core analysis,log, magnetic resonance, rate-controlled mercury penetration, high pressure mercury injection, and observations of scanning electron microscope and thin section. The fine lithic sandstone and fine feldspathic lithic sandstone are the major lithology type of this reservoir which is characterized by low compositional maturity and medium texture maturity. The pore space types of reservoir mainly include the residual of primary intergranular pores, secondary intergranular pores and microfractures. The petrophysical properties of the reservoir are not favorable with low porosity and permeability. The pore structure is complex with medium sorting coefficient, gentle skewness, high displacement pressure, high median pressure, low median radius and efficiency of mercury withdrawal. It is the throat rather than the porosity that controls the permeability of the reservoir because of the small throat radius and high pore throat radio. Affected by the low permeability, the saturation of mobile fluid is low. The compaction and cementation are the key destructive diagenesis and the dissolution is the key constructive diagenesis. They are the major factors that affect the quality of the reservoir. The matrix porosity is 7.13% at the end of the diagenesis evolution of the reservoir. According to the petrophysical properties of reservoir and pore structure parameters, the S1k1 reservoir was classified into 3 types and type I is better than the others.