Abstract: The porosity distributions at different section of thirteen sandstone cores were studied by using the X-ray CT scanning system. The 3-D distributions of the core porosity were determined with the 3-D reconstruction technique. The porosity distributions and heterogeneity of those cores were observed clearly in the level of "pore group". The observed porosities at different section were analyzed and characterized quantitatively with the statistics method. Three scanned cores were taken as the example to show the porosity distributions. The obvious stratification phenomena exist in the S138 core, and the heterogeneity is serious. The standard deviation and nonuniform coefficient are great. The porosity distribution is uneven, and the pore sorting is bad. There are more low-porosity areas and less high-porosity areas in each section of the No.71 core, and the average porosity of the core is lower. There are more high-porosity areas and local low-porosity areas at each section of the S35 core. The average porosity of this core is high, and the core is homogenous. The standard deviation and nonuniform coefficient are lowest, and the pore distribution is uniform. The pore sorting of this core is good.