Abstract: Through systematic drilling,well logging,seismic data analysis of 9-area in Tahe oilfield,combined with core observation,thin section identification and geochemical analysis,the gas-bearing layers of ordovician condensate gas reservoir of 9-area in Tahe oilfield is mainly from Yijianfang formation,part from Yingshan formation,with mainly micrite and secondly grain limestone.The physical property of reservoir matrix is poor and the main reservoir space types are mainly caves and cracks,the pore-types are less,and there are three reservoir types,namely crack-hole type,cavity type and crack type.The reservoir development is controlled by local structure,faulting,fracture and karstification.Karstification is essential to the reservoir development,and the karstification in structural high position is strong,with developed reservoirs.On the plane,the fracture and fracture systems can provide seepage channels for karstification,the favorable reservoir body presents plate shaped distribution along the fracture and the tangent place of the fracture.Vertically the favorable reservoirs are mainly located in calcarenite section 0~60 m below ordovician Yijianfang formation,and under atmospheric water karstification control of normal phreatic surface.