Abstract: A detailed study is carried out on the diagenesis and pore evolution with thin section observation, X-ray diffraction, scanning transmission electron microscope and vitrinite reflectance. The results show that the rock type of the 2nd and 3rd members of Liushagang Formation in the Wushi Sag is dominated by quartz sandstone, with minor feldspathic quartz sandstone. The size fraction of grains is moderate to poor. The diagenesis of the sandstone has reached to Stage A of the middle diagenetic period. The pores are mainly primary intergranular and secondary dissolution types. The primary intergranular pores decrease with the compaction and cementation of sandstone, while the secondary pores increase with dissolution, which improve the physical property of reservoir.