The invention relates to a preparation method for a zinc-nickel-cobalt subcarbonate supported photoelectrode. The preparation method comprises the following steps that a layer of titanium oxide nanorod array is formed on the surface of a conductive substrate; zinc organic salt, nickel organic salt, cobalt organic salt and urea are mixed to be uniform in water, and a mixed solution is obtained; and the treated conductive substrate is immersed into the mixed solution, a reaction occurs at the temperature from 60 DEG C to 90 DEG C, and the zinc-nickel-cobalt subcarbonate supported photoelectrode is obtained. According to the preparation method, the process is simple, raw materials are sufficient, the cost is low, mass production is facilitated, and huge potential application value is achieved. According to the semiconductor photoelectrode prepared through the method, the specific area of the photoelectrode is effectively increased, and the area, making sufficient contact with an electrolyte, of the photoelectrode is increased; and meanwhile, compared with a traditional single-semiconductor electrode, the photoelectrode has the beneficial effects that the introduction of a co-catalyst effectively promotes holes and the electrolyte to react, electron hole pair separation is advantageously improved, and the photocatalytic water splitting efficiency is effectively improved.