Atomically　precise　metal　nanoclusters　(NCs)　have　garnered　tremendous　attention　as　light-harvesting　antennas　in　heterogeneous　photocatalysis　due　to　unique　atomic　stacking　mode,　quantum　confinement　effect,　and　enriched　active　sites.　However,　metal　NCs　as　photosensitizers　suffer　from　extremely　short　carrier　lifetime,　poor　photostability,　and　difficulty　in　carrier　migration,　which　hinder　the　wide-spread　utilization　of　metal　NCs　in　solar　energy　conversion.　To　solve　these　problems,　herein,　Ag-doped　glutathione　(GSH)-capped　gold　NCs,　i.e.,　alloy　Au1−xAgx@GSH　NCs　and　non-conjugated　insulating　polymer　of　poly(diallyl-dimethylammonium　chloride)　(PDDA)　are　utilized　as　the　building　blocks　for　layer-by-layer　assembly　of　spatially　multilayered　alloy　NCs/metal　oxide　(MO)　photosystems.　The　alternately　deposited　ultrathin　PDDA　layer　in-between　Au1−xAgx@GSH　NCs　on　the　MO　substrate　functions　as　an　efficient　charge　flow　mediator　to　relay　the　directional　photoelectron　transfer　over　Au1−xAgx@GSH　NCs,　giving　rise　to　the　cascade　charge　transfer　chain.　This　peculiar　carrier　migration　mode　endowed　by　exquisite　interface　configuration　design　significantly　boosts　the　unidirectional　electron　migration　from　the　Au1−xAgx@GSH　NCs　to　the　MO　substrate,　substantially　improving　the　visible-light-driven　photoelectrochemical　water　oxidation　performances　of　MO/(PDDA-Au1−xAgx)n　multilayer　heterostructured　photoanodes.　The　work　will　inspire　the　rational　construction　of　alloy　metal　NCs-based　photosystems　for　modulating　spatially　controllable　charge　transfer　pathway　for　solar　energy　conversion.　©　2023　Wiley-VCH　GmbH.