Abstract: We studied the relationship between authigenic chlorite content in sandstone and the parameters of pore structure by thin section analysis, XRD, SEM, physical property analysis and mercury intrusion analysis on 10 samples in Longdong area of Ordos basin. The result indicates that, when sandstone porosity changes little, with increasing authigenic chlorite content, the permeability of the sandstone decreases while drainage pressure and median pressure increase, and the corresponding throat radius decreases obviously; meanwhile, throat mean value and the number of throats in different types also decrease significantly. Our research results also indicate that although the increasing of authigenic chlorite content would ameliorate the sorting and heterogeneity of throats, the number of large throats would reduce correspondingly; furthermore, the increasing of authigenic chlorite content would remarkably reduce ejection efficiency. Therefore, increasing pore-lining authigenic chlorite would reduce the quality of sandstone reservoirs and affect hydrocarbon exploitation under the prerequisite of similar porosity.