On the basis of X-ray diffraction of clay minerals, analysis of resin-cast thin sections of cores, and scanning electron microscope (SEM) observation of samples in central Sichuan Basin, this paper studies the microscopic characteristics and occurrences of chlorite and the relationship between its genesis and reservoir development. The chlorite in central Sichuan Basin is mainly trioctahedron ferrum-magnesium transition chlorite, with ferrum being a little higher. It occurs as grain-coatings and pore linings and is mostly formed during the middle stage of diagenesis, closely related to ferrum-rich depositional environment. The chlorite content in the study area is positively related to porosity and permeability. The distribution and occurrence of chlorite plays an important role in affecting the porosity and permeability of reservoirs. Pore-lining and grain-coating chlorite and its overgrowth during diagenesis enhance the mechanical strength of rock and its ability of resistance to compaction. The chlorite also isolates detrital quartz surfaces from contact with pore water, thus preventing nucleation of authigenic quartz and consequently preserving pores in sandstone.