Abstract: Chang 4+5oil reservoir is one of the important new strata product replacements in ZhenbeiHuanxian area of Ordos Basin.By the research of the reservoir petrology and physical properties and pore structure and influential factor of reservoir,the composition of the rock types are mainly feldspathic lithic sandstone and lithic sandstone,and the pore types are mainly intergranular pore and dissolved pore and the pore combination with small pore and fine throat.Mercury injection experiment shows that better pore structure,mainstream throat radius,the reservoir overall is relatively good.Average porosity and permeability are 11.5% and 1.47×10^-3 μm².The cause of relatively high permeability reservoir is the main sedimentary and diagenesis,among them the sedimentation controlls the distribution of sand bodies and growth is relatively high permeability reservoir in the main part of the river which influences the particle size of sandstone body composition and sand reservoir properties.Favorable diagenesis controlls the distribution of relatively high permeability reservoir,with strong corrosion,weak compaction and cementation.It is an important cause leading to relatively high permeability reservoir in Zhenbei-Huanxian area.