On the basis of field outcrop profile and core observation in combination with thin sections, SEM (scanning electron microscope), CL (cathodoluminescence) and physical property analysis, this paper studied in detail the reservoir characteristics of the Permian Changxing Formation in Jiannan area. The reservoir is mainly composed of reef dolostones, reef limestones and grained dolostones, and the reservoir spaces mainly include intercrystal pores, intercrystal dissolved pores and cracks, suggesting a crack-pore reservoir. The reservoir is of moderate-bad physical property, belonging to the low porosity, moderate-low permeability reservoir. The reservoir formation is controlled by lithology, sedimentary facies, relative sea level change and diagenesis. The platform edge reef-bank is in favor of reservoir development, corresponding to the lowering of the relative sea level, and the rocks are mainly reef dolostones and reef limestones. Dolomitization is the foundation of reservoir formation, whereas dissolution and fracturing are the keys to improving physical properties. In this paper, porosity and permeability were used to synthetically evaluate Changxing Formation reservoir, and the results indicate that Type Ⅲ (low porosity-low permeability) is the major reservoir type, followed by Type Ⅳ (particularly low porosity-particularly low permeability), whereas Type Ⅱ (moderate porosity- moderate permeability) and Type Ⅰ (high porosity- high permeability) are rarely seen.