The　particle　size　of　co-catalysts　significantly　affects　the　activity　of　semiconductors　in　photocatalysis.　Herein,　we　report　that　the　photocatalytic　H-2　evolution　(PHE)　activity　of　a　visible　light　responsive　covalent　organic　framework　(COF)　layer　supported　on　SiO2　nanoparticles　was　greatly　promoted　from　47.7　to　85.5　mu　mol/h　by　decreasing　the　particle　size　of　the　Pd　co-catalyst　from　3.3　nm　to　single　atoms/clusters.　A　PHE　rate　of　156　mmol　gCOF(-1)　h(-1)　and　apparent　quantum　efficiency　up　to　7.3%　were　achieved　with　the　Pd　SAs/Cs　cocatalyst.　The　relationship　between　the　activity　of　Pd　in　H-2　dissociation,　proton　reduction,　and　PHE　rate　suggests　that　the　promotion　effect　of　Pd　SAs/Cs　is　mainly　attributed　to　their　enhancement　in　charge　separation　of　COF　layers　rather　than　proton　reduction.　Furthermore,　a　photoactive　film　was　fabricated　and　steady　production　of　H-2　was　achieved　under　visible　light　irradiation　and　static　conditions.　The　optimization　of　the　particle　size　of　co-catalysts　provides　an　efficient　method　for　enhancing　the　photocatalytic　activity　of　semiconductors.