Abstract: Western Nanliang area is located in southwestern Shanbei slope of the Ordos Basin, and Chang 6 oil-bearing formation is its main exploration target. Delta front subfacies is developed in the northeast and deep lake facies occurs in the south of the study area. The sandstone reservoir is composed of arkose sandstone and lithic arkose sandstone. The main types of cements include calcite cements, illite cements, chlorite cements and siliceous cements. All of these cements reduce the reservoir quality of the sandstone. The authors have reached the conclusion that Chang 6 oil-bearing formation is a low porosity and ultra-low permeability reservoir, as evidenced by studying the property parameters such as porosity and permeability. According to capillary pressure curves, the pore throat structure is of type Ⅱ. Diagenesis is the main factor influencing the reservoir property.