Abstract: The characteristics and genesis of the middle to deep reservoir rocks in the Kekeya structure, Taibei depression, Xinjiang are examined in the light of thin-section examination, SEM, energy spectrum and physical properties. The reservoir rocks in the Badaowan Formation in the Kekeya structure consist almost of clastic rocks, and are characterized by grey, dark grey or greyish black medium-to thick-bedded muddy siltstone, medium-to coarse-grained sandstone and gravel-bearing coarse-grained sandstone with abundant charcoal. The porosity types contain intragranular solution openings and intergranular residual solution openings. The diagenesis contains compaction, cementation and dissolution. These reservoir rocks have extra-low porosity and extra-low permeability caused by the deposition in the study area. The diagenesis is believed to be the key factor for the formation of the dense medium-deep reservoir rocks, and grain sizes are interpreted as main controlling factors for the reservoir quality. The results of research in this paper may provide a reference in improving exploration success in the deep reservoir rocks in China and other parts of the world.