Visible　light-driven　photocatalytic　H-2　production　from　seawater　faces　challenges　from　the　dissolved　salts　in　seawater,　which　would　lead　to　undesirable　decomposition　of　catalysts　and　side　reactions.　Herein,　we　show　a　thioether-functionalized　covalent　organic　framework　(TTR-COF),　which　exhibits　remarkable　photocatalytic　H-2　production　ability　from　seawater.　With　the　specific　affinity　of　thioether　groups　for　Au　ions,　TTR-COF　shows　selectivity　in　adsorption　of　Au　over　other　alkaline　and　alkaline-earth　metal　cations　in　seawater,　which　is　critical　for　uniform　loading　of　Au　as　a　cocatalyst　for　efficient　charge　transfer.　Besides,　the　highly　conjugated　structure　containing　triazine　units　in　TTR-COF　contributes　to　the　visible　light　harvesting　and　photoinduced　charge　generation　and　separation.　The　crucial　synergistic　effects　endow　TTR-COF　with　selective　coordination　to　cocatalysts　over　other　cations,　as　well　as　superior　catalytic　stability　among　other　COFs.　These　suggest　that　COFs　have　great　potential　for　photocatalytic　H-2　production　from　seawater　by　taking　advantage　of　their　unique　structural　features.