In　this　work,　Ag　and　Pt　were　compared　as　a　co-catalyst　on　graphitic　carbon　nitride　(g-C3N4)　for　the　enhanced　photocatalytic　activity　of　water　spilitting　into　hydrogen　generation.　In　order　to　prepare　Ag/g-C3N4　and　Pt/g-C3N4,　initial　adsorption　of　noble　metal　ions　was　performed　on　the　g-C3N4　surface,　followed　by　reducing　them　by　using　NaBH4.　Decoration　of　Ag　or　Pt　nanoparticles　on　g-C3N4　can　extend　the　visible　light　adsorption　and　promote　segregation　of　the　photogenerated　carriers,　which　contribute　to　an　improved　photocatalytic　performance.　Pt/g-C3N4　has　a　higher　photocatalytic　activity　in　water　spilitting　for　H-2　generation　(841　mu　mol　g(-1)　h(-1))　than　that　of　Ag/g-C3N4　(305　mu　mol　g(-1)　h(-1)),　however,　almost　no　H-2　generation　for　pure　g-C3N4.　For　checking　the　photogenerated　holes,　(OH)-O-center　dot　generation　rate　was　tested　by　using　the　reaction　of　terephthalic　acid　(TA)　with　(OH)-O-center　dot　to　form　2-hydroxy-terephthalic　acid　(TAOH).　On　the　basis　of　experimental　results　and　theoretical　calculation,　a　possible　photocatalytic　mechanism　is　put　forward.　It　is　suggested　that　Pt　can　play　a　better　role　as　the　co-catalyst　than　Ag　can,　due　to　the　d-centre　of　Pt　is　closer　to　Fermi　level　than　that　of　Ag　on　the　g-C3N4　surface,　which　can　promote　the　charge　separation　and　accelerate　the　electron　transformation.