The invention relates to a preparation method of a low-dimensional tantalum-based nano-array photo-electrode. The invention belongs to the field of solar energy, photo-catalyzing, and photochemical material. A metal tantalum foil is adopted as an initial raw material, and is mixed with hydrofluoric acid, hydrogen peroxide, cobaltate, cuprate, and the like; a constant-temperature reaction is carried out in an autoclave, such that a metal-oxide-loaded photo-electrode with the tantalum foil as a substrate and with a low-dimensional tantalum-based nano-array uniformly grown on the surface is obtained; the photo-electrode is washed by using ethanol and water, and is dried; the photo-electrode is further delivered into a heat treatment furnace, such that nitriding heat treatment is carried out; through the controlling over the ratio and flow rates of ammonia and water vapor, and through different periods of time, oxynitride and nitride array photo-electrodes with different nitrogen contents can be obtained; with a spin-coating method, graphene or nitrogen-doped graphene is uniformly covered on the surface of the nano-array. The photoelectric conversion efficiency of the tantalum-based composite nano-array photo-electrode is substantially improved. The visible-light-response tantalum-based composite nano-array photo-electrode provided by the invention has high Light-quantum conversion efficiency, and can be used in solar energy conversion and utilization.