Abstract: In this article,highly ordered TiO₂ nanotube arrays were prepared by electrochemical anodization.The concept of‘mergers’ was proposed.pH gradient theory put forward by Macak was verified with SEM images and the formation mechanism of ‘mergers’ of titania nanotubes was explained by the effect of electric double layer.The reasons of the further augment of orig-inal nanotubes' diameters were also analyzed.