Nanowire (NW) structures is an alternative candidate for constructing the next generation photoelectrochemical water splitting system, due to the outstanding optical and electrical properties. NW photoelectrodes comparing to traditional semiconductor photoelectrodes shows the comparatively shorter transfer distance of photo-induced carriers and the increase amount of the surface reaction sites, which is beneficial for lowering the recombination probability of charge carriers and improving their photoelectrochemical (PEC) performances. Here, we demonstrate for the first time that super-long Cu2O NWs, more than 4.5 μm, with highly efficient water splitting performance, were synthesized using a cost-effective anodic alumina oxide (AAO) template method. In comparison with the photocathode with planar Cu2O films, the photocathode with Cu2O NWs demonstrates a significant enhancement in photocurrent, from –1.00 to –2.75 mA/cm2 at –0.8 V versus Ag/AgCl. After optimization of the photoelectrochemical electrode through depositing Pt NPs with atomic layer deposition (ALD) technology on the Cu2O NWs, the plateau of photocurrent has been enlarged to –7 mA/cm2 with the external quantum yield up to 34% at 410 nm. This study suggests that the photoelectrode based on Cu2O NWs is a hopeful system for establishing high-efficiency water splitting system under visible light.