Improving the Pt atoms utilization efficiency on self-supported electrodes is crucial for industrial seawater hydrogen production, but effective strategies are still lacking. Herein, we reported a novel strategy to anchor highly surface-exposed Pt single atoms on NiS/CoS with abundant S vacancies (Pt–NiS/CoS–Sv) as a self-supported electrode. Physical characterizations and theoretical calculations confirm that the strong Pt–S electron bridges with the coordinating role of surface S vacancies triggers the d-orbital electron rearrangements and regulates the local electron structures between the Co/Ni and Pt sites. Notably, the Pt–NiS/CoS–Sv electrode displays an ultralow overpotential of 18 mV at 10 mA cm in alkaline seawater. More importantly, our Pt–NiS/CoS–Sv electrode assembled into an alkaline electrolysis cell can work continuously for 50 h under alkaline seawater @ 60 °C. This work provides a promising strategy for designing highly surface-exposed single-atomic catalyst for large-scale hydrogen evolution through seawater electrolysis.