Abstract: Based on detailed core observation, thin?section identification and sample analysis and test of 5 wells drilled in Wushi sag of the west end of Kuqa depression in Tarim basin, it is recognized that the Mesozoic reservoir in this sag are all clastic rocks, dominated by debris sandstone; the reservoir spaces are dominated by intergranular dissolution pore, intragranular pores and intercrystal pore, with a few fracture pore, belonging to a medium?low porosity and low permeability reservoir as a whole. Comprehensive analysis reveals that the development of the reservoir is obviously controlled by the sedimentation and diagenesis. And the braided river delta plain sand body, the braided river delta front sand body and the fan delta front sand body are its dominant lithofacies, while the dissolution is the most important constructive diagenesis. It is concluded that the clay interstitial and grain supported sandstone could be the most favorable reservoir and the adjacent major faults which communicate with the oil source is easy to form advantageous hydrocarbon traps in this area