Charge　separation/transfer　is　generally　believed　to　be　the　most　key　factor　affecting　the　efficiency　of　photocatalysis,　which　however　will　be　counteracted　if　not　taking　the　active　site　engineering　into　account　for　a　specific　photoredox　reaction.　Here,　a　3D　heterostructure　composite　is　designed　consisting　of　MoS2　nanoplatelets　decorated　on　reduced　graphene　oxide-wrapped　TiO2　nanotube　arrays　(TNTAs@RGO/MoS2).　Such　a　cascade　configuration　renders　a　directional　migration　of　charge　carriers　and　controlled　immobilization　of　active　sites,　thereby　showing　much　higher　photoactivity　for　water　splitting　to　H2　than　binary　TNTAs@RGO　and　TNTAs/MoS2.　The　photoactivity　comparison　and　mechanistic　analysis　reveal　the　double-edged　sword　role　of　RGO　on　boosted　charge　separation/transfer　versus　active　site　control　in　this　composite　system.　The　as-observed　inconsistency　between　boosted　charge　transfer　and　lowered　photoactivity　over　TNTAs@RGO　is　attributed　to　the　decrease　of　active　sites　for　H2　evolution,　which　is　significantly　different　from　the　previous　reports　in　literature.　The　findings　of　the　intrinsic　relationship　of　balanced　benefits　from　charge　separation/transfer　and　active　site　control　could　promote　the　rational　optimization　of　photocatalyst　design　by　cooperatively　manipulating　charge　flow　and　active　site　control,　thereby　improving　the　efficiency　of　photocatalysis　for　target　photoredox　processes.　©　2018　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim