Based on a large number of core and thin section data, seven microfacies types of the Upper Cretaceous Khasib Formation of Iraq A Oilfield are identified through the study of sedimentary fabric, biological association and diagenesis, and the carbonate ramp sedimentary model of Khasib Formation is established. Combined with reservoir physical property and mercury injection data, through the analysis of pore type, physical property characteristics and pore structure difference, the reservoir of Khasib Formation is divided into four types: high porosity and high permeability, high porosity and medium permeability, high porosity and low permeability, and low porosity and low permeability. Based on quantitative-semi-quantitative analysis of sedimentary fabric, it is shown that sedimentary fabric has an important influence on reservoir permeability, and the contents of green algae and intraclast are directly proportional to reservoir permeability, and the content of lime mud is inversely proportional to reservoir permeability. It is suggested that the bottom water injection should be considered in the process of development for high porosity and high permeability reservoirs, and high porosity and medium permeability reservoirs. As potential reservoirs, high porosity and low permeability reservoirs can be produced by horizontal well acidizing fracturing and other reservoir reconstruction technologies. The low porosity and low permeability reservoir can be used as the cap rock of high quality reservoir in the lower part.