Abstract: With the increase of the anodizing time, the nanoporous morphology of the anodic porous alumina film formed by anodizing Al in an oxalic acid solution will change from irregular to regular and the distribution of nanoporous will also change from disarray to regular hexangular array. The results indicated that there was high internal stress in the barrier layer due to the severe mismatch between the barrier layer formed in early anodization and the Al substrate. The release of the internal stress resulted in the origination of the numerous nanoporous in the surface of the barrier layer, which accordingly made the surface energy of oxide film increase quickly. The internal stress in the walls and the surface tension in the surface of nanoporous acted together in the anodization and determined the morphology and distribution of the nanoporous in each phase of the anodization. When these two forces reached a balance, the nanoporous possessed excellent uniformity in diameter and spacing of the holes. At this time, the energy of the system is at the lowest. The transition process from unbalance to balance of the these two forces is the internal drive in the selforganized process of the porous configuration from the initial irregular through to regular array.