Visible　light-driven　photocatalytic　H2　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　H2　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　H2　production　from　seawater　by　taking　advantage　of　their　unique　structural　features.　©　2019　American　Chemical　Society.