The full utilization of incident light is vitally important for boosting the photoelectrochemical activity of photoelectrodes. Herein, we introduce Ni-BiVO4 nanoarrays for mediating the photoelectrochemical water splitting by optimizing the optical modes. Highly ordered Ni-BiVO4 nanoarrays were fabricated using a nanoimprinted AAO templating technique. By controlling the thickness of BiVO4, we efficiently regulate the photoelectrochemical activity, and the photocurrent was up to 0.91 mA cm-2 at 1.4 V versus Ag/AgCl under 100 mW cm-2 in the visible light, which is 3.25 times that of a flat Ni-BiVO4 electrode with the same deposition cycles of BiVO4. The optimal efficiency of a Ni-BiVO4 nanoarrray-based photoelectrode can be attributed to the optimal morphology, which has the lowest reflection, the strongest scattering and the induced strongest absorption for the incident light among the nanoarrays samples with different thickness of BiVO4. This work demonstrates the importance of the optimization of optical modes in the nanoarray photoelectrode in order to boost photoelectrochemical activity.