Although　Schottky　barriers　at　the　interface　of　metal/semiconductor　help　electron/hole　separation　in　photo-catalysis,　they　also　limit　the　migration　of　electrons　across　the　interface.　Herein,　we　tune　Schottky　barriers　over　Ni/S　vacancy-rich　Mn0.3Cd0.7S　(Ni/MCS-s)　composites　prepared　by　self-assembly　and　photochemical　method.　The　Ni/MCS-s　heterostructures　exhibits　superior　hydrogen　production　activity　up　to　164.1　mmol/h/g　in　simulated　seawater　(3.5　wt%　NaCl),　which　is　68　and　5　times　higher　than　MCS-s　and　1　wt%　Pt/MCS-s,　respectively.　The　apparent　quantum　yield　reached　60.4%　at　420　nm.　The　excellent　photocatalytic　performance　of　Ni/MCS-s　results　from　the　coupling　of　plasmonic　Ni　and　S　vacancies,　which　can　effectively　lower　Schottky　barrier　and　enhance　hot　electrons　across　the　interface　for　photocatalytic　process.　Moreover,　the　Ni　layer　effectively　prevents　the　catalyst　from　being　corroded　in　seawater.　This　work　provides　a　feasible　strategy　for　designing　efficient　photocatalysts　for　solar　energy　conversion　in　seawater.