The Middle-Sha-3 Formation in Wennan Oilfield is in weak oxidation - reduction environment of delta front, shore and shallow lake sedimentary system and in reducing environment of half deep lake and deep lake facies sedimentary system.Reservoir lithology is mainly composed of lithic arkose and arkose. The difference of lithology and physical property influence the oil/gas accumulation level and regularity of distribution. The clastic composition and content and cement composition and contend are the main factors of controlling physical property of oil reservoir. Oiliness of different lithology is different, and oiliness of feldspathic fine-grained sandstone and silty sandstone is best. The lithology, physical property, electrical property and oiliness of the 2-4 Sand Groups of the Middle-Sha-3 Formation in Wennan Oilfield were analyzed by data of drill core, well logging and analysis testing. Their inner relation are received, and the good interpretation models of porosity, permeability, and oil saturation were established, the cross plot of oil testing, physical property and electrical parameters was made and the quantitative interpretation standard of oil reservoir for the 2-4 Sand Groups of the Middle-Sha-3 Formation in Wennan Oilfield was determined to divide oil layer, acquifer and dry layer. Therefore it provides the reliable basis for the development and evaluation of oil and gas in this area.