Abstract: The Upper Paleozoic reservoirs in the Daniudi Gas Field are characterized by low porosity and low permeability.The physical property of the 3rd and 2nd members of Lower Shihezi Formation is the best,while that of the 1st member of Shanxi Formation is worse,and that of the 2nd member of Shanxi Formation and the 1st member of Lower Shihezi Formation is the worst.The difference of physical property is influenced by several factors such as sedimentary facies,diagenesis,clay mineral,fissure and so on.Sedimentary facies is the basic factor.Meandering sand body has the best physical property,braided fluvial sand body the second,and delta channel sand body the worst.Diagenesis also plays an important role,especially the compaction effect.From the 1st member of Shanxi Formation to the 3rd member of Lower Shihezi Formation,as the compaction effect decreases,the surplus interparticle porosity of reservoir increases and the physical property is improved.Clay mineral composition,content and fissure also influence physical property.Generally speaking,higher illite content results in worse property,and the generation of microfracture may improve property.