Construction　of　graphene-based　composites　has　been　a　popular　theme　in　solar　energy　harvesting　and　conversion,　yet　the　understanding　of　the　real　efficacy　of　graphene　for　enhancing　photocatalytic　efficiency　is　hampered　by　the　gap　of　physicochemical　properties　between　the　defined　graphene　and　the　graphene　used　in　research　laboratories.　Here,　we　purposely　synthesize　a　high-quality　chemical　vapor　deposition　graphene　(CVDG)　as　a　model　material　to　integrate　with　TiO2,　which　demonstrates　that　photocatalytic　performance　can　be　greatly　improved　by　controlling　the　quality　of　graphene.　Under　the　same　reaction　conditions,　the　as-prepared　CVDG-TiO2　displays　a　26.2-times　and　10-times　higher　photocatalytic　hydrogen　evolution　activity　than　bare　TiO2　and　its　counterpart,　reduced　graphene　oxide　(RGO)-TiO2,　respectively.　Experimental　characterization　reveals　that　the　few-layer　CVDG　with　a　low　defect　density　is　able　to　better　unleash　the　excellent　electrical　conductivity　potential　of　graphene,　by　which　the　separation　and　lifetime　of　photoexcited　charge　carriers　of　graphene-TiO2　could　be　improved　more　efficiently.　The　research　highlights　the　significant　effect　of　the　quality　of　graphene　for　the　construction　of　more　efficient　semiconductor-graphene　composites,　which　is　anticipated　to　inform　ongoing　efforts　on　exploiting　high-quality　graphene　to　advance　solar　energy　harvesting　and　conversion.