Silicon nanowire arrays (SiNWs) have shown great potential as water splitting materials because of their excellent light absorption ability and high surface area-to-volume ratio, which promote photoelectrochemical reactions. However, the catalytic activity of SiNWs for hydrogen evolution is hindered by slow charge transfer kinetics. Herein, we propose a new approach to boost hydrogen production in simulated seawater by employing NiSx cocatalyst-decorated SiNWs photocathodes. The integration of NiSx cocatalyst onto SiNWs significantly improves the catalytic performance and stability, enabling efficient hydrogen evolution under simulated sunlight irradiation. The HER performance of NiSx/SiNWs photocathodes was systematically investigated in simulated seawater. The optimized photocathode exhibited an onset potential of 0.068 V vs. RHE while the SiNWs photocathode showed an onset potential at -0.597 V vs. RHE. Besides, a remarkable hydrogen evolution rate of 189.15 μmol‧h-1‧cm-2 was obtained, which is 30.86 times higher than that of pristine SiNWs. Systematically experimental investigations confirmed that the in situ-grown nickel sulfide (NiSx) provides abundant active sites for HER, enhancing electrocatalytic activity while simultaneously acting as a passivation layer to mitigate alkaline electrolyte-induced photodegradation of the silicon surface. These noteworthy advancements significantly elevate the HER performance of the photocathode. Our findings underscore the potential of this hybrid photocathode system for sustainable hydrogen production from abundant seawater resources.