Pore structures and their changes of ordinary strength concrete and high strength concrete at different curing ages of 3, 28, 90d were studied using thermoporometry, and the results were compared with those from MIP and NAD. The relationship among micro pores and porosity of concrete and its macroscopic properties was also studied. The results indicate that compared to MIP, thermoporometry can characterize the features of pores with the diameter smaller than 100nm in concrete accurately. The differences of macroscopic mechanical properties of concretes can be explained using the changes of their pore size distribution. After curing age of 28d, the amount of pore with the diameter larger than 20 nm in high strength concrete changes little, but it decreases gradually in ordinary strength concrete. And pores with diameter smaller than 20 nm in concrete have little influence on the macroscopic mechanical property of concrete.