Nanometer pore structure of shale reservoir is of great importance for both shale hydrocarbon evaluation and exploration. But currently, the research of shale nano pore structure of sedimentary basins is relatively insufficient. This paper analyses the Shale nanopore structure characteristics of Xujiahe Formation of Upper Triassic in western Sichuan basin by using the methods of low temperature nitrogen adsorption and scanning electron microscopy. The results are the following. First, shale specific surface area of western Sichuan basin Xujiahe Formation is in scope of 6.588m2/g-9.476m2/g provided by transitional span and micro pore, which is larger than tight sandstone specific surface area. Second, the average of shale aperture is in range of 4.319nm~7.821nm. The pore is a series of successive pore range from micropore to mesopore. There are different types of pore shape. Micro pore is mainly of unilateral closed hole and ink bottle type hole, while transitional pore and mesopore has a certain amount of open rack holes on both ends. Third, organic nanopore grown from sale and clay mineral interganular pore dominatingly provides the natural gas adsorption sites. Mineral interganular pore and microcarcks are the main occurrence places of free gas and provide natural gas seepage channel.