The invention discloses a hydrothermal method-based method for preparing a alpha-Fe2O3 nanotube array. The method comprises the following steps: preparing a beta-FeOOH nanorod array, namely obliquely placing a glass substrate coated with fluorine-doped stannic oxide (FTO) in a mixed liquid of FeCl3 and NaNO3, and performing hydrothermal reaction at 100 DEG C for 12h so as to obtain a beta-FeOOH nanorod array which grows on the glass substrate; and preparing the alpha-Fe2O3 nanotube array, namely annealing the beta-FeOOH nanorod array in nitrogen gas for 6h so as to obtain the alpha-Fe2O3 nanotube array. The method is high in preparation efficiency, short in production period, low in production cost, low in device requirments, and easy to operate, has effects of environment friendliness and no pollution and is suitable for mass production.