On the basis of thin section,scanning electron microscopy,physical property analysis andmercury injection analysis,the reservoir characteristics and main control factors of Triassic clastic res-ervoir in Southern Qilian Basin were studied.The results indicate that the cIastic reservoir sandstoneis mainly composed of medium to fine grained feldspar sandstone and the textural and compositionalmaturation of the reservoir is low.The main reservoir space types are interstitial content pores,disso-lution pores and fractures.In additional,the reservoir pore structure is characterized by mini porethroat,poor sorting,poor connectedness and poor infiltrating ability.The reservoir physical propertiesare poor,with low porosity and Iow permeability.Moreover,the development of reservoir is mainlycontrolled by sedimentation,diagenism and favorable tectonic condition.Comprehensively consideringabove analysis,the Triassic clastic reservoirs have been divided into type V,type V[ and type V1I,o-verall belonging to tight reservoirs with ultralow porosity and permeability.