Covalent　organic　frameworks　(COFs)-based　photocatalysts　have　received　growing　attention　for　photocatalytic　hydrogen　(H-2)　production.　One　of　the　big　challenges　in　the　field　is　to　find　ways　to　promote　energy/electron　transfer　and　exciton　dissociation.　Addressing　this　challenge,　herein,　a　series　of　olefin-linked　2D　COFs　is　fabricated　with　high　crystallinity,　porosity,　and　robustness　using　a　melt　polymerization　method　without　adding　volatile　organic　solvents.　It　is　found　that　regulation　of　the　spatial　distances　between　the　acceptor　units　(triazine　and　2,　2＇-bipyridine)　of　COFs　to　match　the　charge　carrier　diffusion　length　can　dramatically　promote　the　exciton　dissociation,　hence　leading　to　outstanding　photocatalytic　H-2　evolution　performance.　The　COF　with　the　appropriate　acceptor　distance　achieves　exceptional　photocatalytic　H-2　evolution　with　an　apparent　quantum　yield　of　56.2%　at　475　nm,　the　second　highest　value　among　all　COF　photocatalysts　and　70　times　higher　than　the　well-studied　polymer　carbon　nitride.　Various　experimental　and　computation　studies　are　then　conducted　to　in-depth　unveil　the　mechanism　behind　the　enhanced　performance.　This　study　will　provide　important　guidance　for　the　design　of　highly　efficient　organic　semiconductor　photocatalysts.