The accelerated calcium leaching experiments of cement mortar lining of ductile iron pipe specimen, which is designed and performed under centrifugal casting, were carried out under flowing 6mol/L ammonium chloride solution. The pore structure of cement mortar lining in the process of calcium leaching was investigated by means of mercury intrusion porosimetry(MIP) and X ray computed tomography imaging technology(X CT) for analyzing the evolution of pore structure of cement mortar lining caused by the flowing solution. The results show that the pore structure of cement mortar lining has a great change in the process of the accelerated leaching. After leaching for 150 d, the porosity(by volume) of cement pastes in cement mortar lining increases from 957% to 3549%, and the most probable pore diameter increases from 1711nm to 2630nm, which results in a small amount of damage pore. While the leaching time is 450 d, the porosity of cement pastes in cement mortar lining reaches 6154%, and thus produces a lot of damage pore(single pore size greater than 4×10-6mm3), and the porosity and the number of damage pore of cement mortars in cement mortar lining increase with the leaching time.