The reservoir ability of coal rocks is controlled by both sedimentary facies and diagenesis. Sedimentary facies controls the content of ash and microcomponents of coal rocks, which further affect the reservoir ability of coal beds. There exists quantitative relation between the ash production rate and the porosity and permeability of coal. The more the ash, the lower the porosity and permeability of the coal. Among microcomponents of coal rocks, vitrinite is favorable to formination of cleat, which can enhance the permeability of the coal. The more the vitrinite in the coal, the higher the porosity and permeability. The content of vitrinite and ash are different in different types of coals. From dull coal to bright coal, vitrinite tends to increase, the ash tends to decrease, and the porosity and permeability tend to increase. In the study area, coals were deposited in tidal flats and delta environments. Due to difference in ash content and micro components, coals formed in tidal flats show higher porosity and permeability than those formed in deltas, and those formed in lower delta plain show higher porosity and permeability than those formed in upper delta plain. In addition, due to dissolution of the calcite cement filling fissures, cleats and pores, coal rocks in the vadose and phreatic zones show better reservoir ability, while deeply buried coal beds, due to cementation and compaction, show poor reservoir ability.