Hydrogen,　with　the　merits　of　zero　emissions　and　high　energy　density,　is　one　of　the　promising　green　energy　sources.　Seeking　for　high　efficiency　and　low-cost　catalysts　is　one　of　the　key　issues　for　hydrogen　evolution　and　its　practical　applications.　Nano-structured　metal　co-catalysts　are　widely　used　to　improve　the　photocatalytic　performance　via　surface　electronic　structure/properties　optimization　of　the　catalyst.　Herein,　we　report　ultra-fine　(similar　to　1　nm)　Cu　clusters　decorated　hydrangea-like　TiO2　systems　for　photocatalytic　hydrogen　evolution.　The　pristine　hydrangea-like　TiO2　support　shows　a　promising　performance　of　hydrogen　evolution　(1.8　mmol.h(-1).g(-1)),　which　is　similar　to　10.7　times　higher　than　that　of　the　commercial　P25　(168　mu　mol.h(-1).g(-1)).　After　ultra-fine　Cu　clusters　decoration,　a　maximal　hydrogen　evolution　performance　(3.7　mmol.h(-1).g(-1))　is　achieved　in　the　optimized　system　6Cu-TiO2　(6　wt%).　Experimental　and　theoretical　studies　demonstrate　that　the　ultra-fine　Cu　clusters　decoration　could　promote　the　charge　separation　and　transfer　process　effectively.　The　Cu　clusters　also　act　as　reaction　sites　for　reduction　of　H2O　to　H-2.　These　results　are　of　great　importance　for　the　study　of　Cu-based　co-catalyst　systems　and　also　shed　light　on　the　development　of　other　non-noble　metal　co-catalysts　in　photocatalysis　hydrogen　evolution.