Abstract: Through comprehensive analysis of core,log,cast thin section, scanning electron microscopy, cathodoluminescence,X diffraction,mercury and other data analysis of Yanchang exploration area in southern Ordos Basin,the research on Chang-8 oil reservoir characteristics and its influencing factors analysis of Yanchang exploration area in southern Ordos Basin has been carried out.The results showed that Chang-8 oil reservoirs are mainly of arkose and lithic feldspathic sandstone,with low compositional maturity and medium maturity structure.The pore types of reservoirs are varied,the intergranular pore and feldspar solution openings are of the main reservoir space.The throat type is mainly of small and micro throat and it is a typical low porosity and low permeability reservoir.The reservoirs are obviously affected by sedimentary facies and diagenesis.The most favorable sedimentary microfacies are underwater distributary channel microfacies with big sediment thickness and coarser particle size.Meantime,the constructive and destructive diagenesis has a dual role on reservoir property transformation.Due to dissolution,the constructive diagenesis can make the physical properties better,while due to cementation and compaction,the destructive diagenesis can cause the physical properties deteriorated.