Abstract: The forth member of upper Triassic Xujiahe formation is an important oil/gas bearing segment in Xinchang area of the western Sichuan depression.The studies of the data of core analysis,petrographic thin section,mercury penetration,oil and gas testing and analysis of the forth member of Xujiahe formation sandstone reservoir indicate that the lithology of this reservoir is mainly lithic sandstone and lithic quartz sandstone,characterized by low-medium mineral maturity,medium structure maturity,lower to medium porosity and permeability,poor pore structure and heterogeneity is intense.According to petrophysical properties of reservoir and pore structure parameters,upper and lower of the forth member of Xujiahe formation sandstone reservoir were classified into four types separately.Type I and type Ⅱ reservoirs are the relatively high-quality reservoirs can be taken as the major target zones.