Based on researches by means of the field observation,ordinary thin sections,scanning electron microscope and reservoir property analysis,the authors studied the petrologic and diagenetic characteristics of the Permian clastic rock reservoirs of Xiariha depression in South Qilian basin,and the result shows that clastic rock in this area are mainly composed of quartz sandstone,feldspar quartz sandstone and the feldspar sandstone and have mainly experienced such actions as compaction,cementation,metasomatism and corrosion,with the evolution reaching the middle diagenetic stage A and the middle diagenetic stage B.