Abstract: Based on the theoretical basis of sedimentary petrology, petroleum geochemistry and carbonate reservoir geology, through a lot of drilling core observation, logging analysis, thin sections and scanning electron microscopic identification, physical property and mercury intrusion analysis, the research of dolomite reservoir characteristics and distribution regularity of Ma5-5 reservoir was carried out. The results showed the rock type of reservoir in Ma5-5 were mainly of powder-fine dolomite. The reservoir space was dominated by the intercrystalline pore type, and the fracture-pore type was secondary. The average porosity was 5.41%, and the average permeability was 1.051.05 × 10~(-3)μm~2, which was low porosity and low permeability reservoir. Ma5-5 dolomite was supergene period downward flow of karst water and formation sedimentary micritic limestone formed by the metasomatism of itself, its distribution was closely related with the ordovician weathering crust karst geomorphology, which mainly distributed in the west of Daniudi gasfield, northern karst highland and the eastern, southern karst groove area, central slope hill and slope zone of dolomite low-development.