Abstract: DaNiuDi gas field is a part of TaBaMiao big gas field. The reservoir is the first member of ShanXi formation of Paleozoic Erathem. This paper confirms that it belongs to the low porosity and extraordinarily low permeability reservoir by statistics analyzing based on a great deal of lab data. And analyzed the formative cause from two sides:the diagenesis and the microcosmic pore structure of the reservoir. This paper also analyzing factors which control and affect the reservoir's porosity and permeability in this district.