In view of the problems of the oil yield decline and the rapid water saturation in single well of Zhuang 36 well area in Xifeng Oilfield, Ordos Basin, the logging data, rock section, scanning electronic microscope, X diffraction, grain size analysis and mercury penetration were used to analyze the lithology characteristics, physical properties, pore throat of Chang 81 reservoir. The result shows that Chang 81 reservoir belongs to low-ultra low porosity and low-ultra low permeability reservoir; the main sandstone is fine-grained lithic arkose; the reservoir mainly developed intergranular pore and dissolved pores; the pore throat structure is the type of small pore and micro throat. Sedimentation and diagenesis have impacted on the reservoir properties together, which leads that the physical properties of subsea distributary channel and mouth bar were better than that of channel frank. According to the physical properties and pore structure parameters, the reservoir in the study area can be divided into four types. The typeⅠbelongs to the best reservoirs, The type Ⅱ belongs to the good, the type Ⅲ belongs to the bad and the type Ⅳ belongs to the worst. The water producing wells mainly distributed in the reservoirs of the type Ⅳand type Ⅲ, and the oil yield in the wells of the type Ⅰ is good and stable.