Abstract: Based on analysis of 30 wells data of logging,well logging,oil production test,geophysical,and rock core and rock thin-section observation,the results show dissolved pores and/or caves,factures are the main reservoir spaces with low matrix porosity in Middle Ordovician Yijianfang Formation,Tuofutai area of Tahe Oilfield.On the plane the reservoir types have the feature of "north-south zoning distribution,east-west heterogeneity".The karst reservoirs mainly formed in middle Caledonian and were controlled by such factors as paleo-geomorphology,faults or fractures,lithology and facies,etc.,showing distinct features of fault-controlled and strata-bound.Thus it is predicted that the areas of favorable reservoir rocks would be developed in the congruent sites of the high position of Caledonian paleo-geomorphology,concentration area of faults or fractures and high energy reef-flat facies,which are mainly distributed in the middle and northern part of Tuofutai area.