Negatively　charged　open-framework　metal　sulfides　(NOSs),　taking　advantages　of　the　characteristics　of　excellent　visible　light　absorption,　easily　exchanged　cations,　and　abundant　active　sites,　hold　significant　promise　as　highly　efficient　photocatalysts　for　hydrogen　evolution.　However,　their　applications　in　photocatalytic　hydrogen　evolution　(PHE)　are　infrequently　documented　and　the　corresponding　photocatalytic　mechanism　has　not　yet　been　explored.　Herein,　we　excavated　a　novel　NOS　photocatalyst　of　(Me2NH2)(6)In10S18　(MIS)　with　a　three-dimensional　(3D)　structure,　and　successfully　incorporated　divalent　Co(II)　and　metal　Co(0)　into　its　cavities　via　the　convenient　cation　exchange-assisted　approach　to　regulate　the　critical　steps　of　photocatalytic　reactions.　As　the　introduced　Co(0)　allows　for　more　efficient　light　utilization　and　adroitly　surficial　hydrogen　desorption,　and　meanwhile　acts　as　the　＇electron　pump＇　for　rapid　charge　transfer,　Co(0)-modified　MIS　delivers　a　surprising　PHE　activity　in　the　initial　stage　of　photocatalysis.　With　the　prolonging　of　illumination,　metal　Co(0)　gradually　escapes　from　MIS　framework,　resulting　in　the　decline　of　PHE　performance.　By　stark　contrast,　the　incorporated　Co(II)　can　establish　a　strong　interaction　with　MIS　framework,　and　simultaneously　capture　photogenerated　electrons　from　MIS　to　produce　Co(0),　which　constructs　a　stable　photocatalytic　system　as　well　as　provides　additional　channels　for　spatially　separating　photogenerated　carriers.　Thus,　Co(II)-modified　MIS　exhibits　a　robust　and　highly　stable　PHE　activity　of　similar　to　4944　mu　mol/g/h　during　the　long-term　photocatalytic　reactions,　surpassing　most　of　the　previously　reported　In-S　framework　photocatalysts.　This　work　represents　a　breakthrough　in　the　study　of　PHE　performance　and　mechanism　of　NOS-based　photocatalysts,　and　sheds　light　on　the　design　of　guest　confined　NOS-based　photocatalysts　towards　high-efficiency　solar-to-chemical　energy　conversion.