TiO2 nanotube arrays were fabricated on Si substrate in HF solution with the low concentration of 0.05 wt%. The diameter and the morphology of the TiO2 nanotubes were observed by scanning electronic microscope (SEM). The effects of oxidation voltage and the applying way of voltage on the nanotubes morphology were investigated. The results show that the diameter and the morphology of the TiO2 nanotubes are obviously influenced by the parameters of the oxidation condition. The TiO2 nanotubes with diameters of 120 nm are obtained by applying a voltage of 0.5 V for 28 min in HF solution with the low concentration of 0.05 wt%. The diameter of the nanotubes could be enlarged to a larger range by optimizing the oxidation time. The dense TiO2 nanotubes with diameters ranging from about 100 to 270 nm are fabricated by the two-step anodic oxidation method, which are much better than the TiO2 nanotubes with diameters from about 70 to 100 nm obtained in the organic electrolyte