Three-dimensional　(3D)　ZnO　nanostructures　were　used　as　the　support　for　gold　nanoparticles　(AuNPs)　and　graphite　carbon　nitride　(g-C3N4)　to　form　a　Z-scheme　heterostructure　photoelectrode　(3D　ZnO/Au/g-C3N4)　in　this　work.　The　3D　structure　of　the　ZnO　nanorods　provided　a　directional　channel　for　fast　carrier　transport　and　abundant　reaction　sites.　ZnO　and　g-C3N4　formed　the　Z-scheme　heterojunction,　and　the　AuNPs　sandwiched　between　ZnO　and　g-C3N4　acted　as　the　mediators　and　greatly　reinforced　vector　electron　transfer　in　the　Z-scheme　heterojunction.　Then,　the　3D　ZnO/Au/g-C3N4　photoelectrode　was　applied　to　develop　a　sensitive　photoelectrochemical　(PEC)　biosensor　for　reduced　glutathione　(GSH)　detection.　GSH　can　act　as　a　hole　scavenger　and　reduce　the　recombination　of　photogenerated　electron-hole　pairs,　which　results　in　an　increase　in　the　photocurrent　of　the　system.　The　enhanced　current　showed　good　linearity　with　GSH　concentration　in　the　range　of　7-2000　mu　M,　and　the　system　had　a　limit　of　detection　of　2.3　mu　M.　The　proposed　biosensor　exhibited　good　selectivity　and　reproducibility,　obtaining　satisfactory　results　in　the　analysis　of　the　target　in　human　serum.