Anodic TiO2 nanotubes (ATNTs) have been investigated for many years. However, the kinetics of oxide growth still remains unclear as well as the relationship between structural features and anodizing parameters. Here, the simulation and separation of anodizing current-time curves are proposed to overcome this challenge. A series of constant voltage anodizing processes in different concentrations of NH4F solutions have been compared in detail. The effect of NH4F concentration on the morphological structure and length were systematically investigated. The morphology images show that ATNTs with lotus-root-shaped nanostructure can also be fabricated when the same voltage are adopted in the second-step anodization as the first-step anodization. We separate the total anodizing current into ionic current and electronic current according to a theoretical formula and find a linear relationship between nanotube length and steady-state ionic current. The interesting results indicated that, the growth of nanotubes is more dependent on the ionic current while the surface morphology of TiO2 nanotubes is related to electronic current and high NH4F concentration is beneficial to the growth of ribs around the nanotubes. (C) 2015 Elsevier Ltd. All rights reserved.