Anodic alumina oxide (AAO) templates with multi-branched structure were fabricated in a phosphoric acid. Atomic force microscope (AFM) was utilized to investigate the unstable growth of porous oxide film in initial stage. The morphologies of cross-section of AAO templates at different current density were also studied with FESEM. The results show that the acquired AAO templates are of multi-branched structure with large size. The diameter of pores on outer surface ranges from 150 to 220 nm, and the width of branches from 100-120 nm. This structure can be due to the unstable growth of AAO film in initial stage. Besides, the structure of AAO template is sensitive to the current density and the order degree decreases with the increase of current density: at 1.0A/dm2, most of tubes are not straight and some divided into two branches; at 2.0A/dm2, all tubes grow disorderly and form net-like structure. In this electrolyte, different types of structure of AAO templates can be acquired by adjusting current density, which may be used for the synthesis of new types of nanowires with improved mechanical properties.