Abstract: Reservoir comprehensive evaluation has great meaning for residual oil development in Nanba-xian Oilfield,locating in north margin of the Qaidam Basin,which has been developed for more than 50 years.Feldspar sandstone and debris-arkosic sandstone are the main rock types of the Tertiary reservoir sandstone with high matrix and cement content in detritus in Nanbaxian Oilfield.Well sorted original pore and secondary dissolved pore are the main pore types.Reservoir diagenesis is relatively weak.The separate out of carbonate is the main factor for original pore decrease.Intergranular porosity is the main pore type,which is connected by bend sheet-sheet shape pore throat.The reservoir has middle porosity-middle permeability and well connectivity.Diagenetic facies is early B period,which is favorable for the development of secondary dissolved pores.Comprehensive reservoir analysis by cluster analysis method showed that reservoir type in Nanbaxian Oilfield was mainly type Ⅲ,the next was typeⅡ,while typeⅠ was relatively small.