In the view of the quantitative stereology, the test method of concrete pore structure was analyzed with application of a light microscope and a computer graphics software （Image Pro Plus）. The test range is under mesoscopic level （101600 μm）. For the feasibility of Image Pro Plus analysis of pore structure, the full test process was proposed in detail. In addition, the minimum sample size, which was equal to four in mortar and one in concrete, was determined. The result indicates that Image Pro Plus analysis, as a test method of pore structure of concrete, can be widely used in practice for its significant representativeness and outstanding operability, which contributes to the further study on the relation between pore structure of concrete and macro performances.