A two-step anodization process was used to fabricate wide-range highly ordered porous anodic alumina membrane (PAA) in the electrolyte of oxalic acid through different anodic voltages. The effect of anodic voltage, pretreatments and pore-expanding time on the microstruture of PAA membrane was also studied in the process of two-step anodization. In a certain range, with the increase of anodic voltage, the pore diameter almost increases linearly while the pore density almost decreases linearly. The PAA template with anneal and electropolishing process has better regularity. In a certain time range, the pore diameter increases obviously with the pore-expanding time. It was demonstrated by XRD that the crystal constitution of the PAA without heat treatment was polycrystalline structure which contained Baehmite phase (Al2O3.H2O), Gibbsite phase (Al2O3.3H2O) and θ-Al2O3 phase. After heat treatment at 500°C for 0.5h, only the θ-Al2O3 phase was retained.