An　all-solid-state　metal-mediated　Z-scheme　photoelectrochemical　(PEC)　immunoassay　was　designed　for　sensitive　detection　of　prostate-specific　antigen　(PSA)　by　using　WO3-Au-CdS　nanocomposite　as　photoactive　material　and　copper　ion　(Cu2+)　as　an　inhibitor.　The　Z-scheme　PEC　system　comprising　of　CdS　nanoparticle　(photosystem　I;　PS　I),　WO3　nanorod　(photosystem　II;　PS　II)　and　gold　nanoparticle　(Au　NP;　solid　electron　mediator)　was　reasonably　established　by　a　simple　and　green　synthetic　method.　As　an　important　part　of　Z-scheme　system,　the　sandwiched　gold　nanoparticles　between　electron　donor　materials　and　hole　provider　materials　could　accelerate　electron　transfer　from　positive　conduction　band　(CB)　of　WO3　to　negative　valence　band　(VB)　of　CdS,　thus　resulting　in　high-efficient　separation　of　the　carriers.　In　the　presence　of　target　PSA,　a　sandwiched　immunoreaction　was　executed　between　capture　antibody-coated　microplate　and　CuO　nanoparticle-labeled　detection　antibody.　Thereafter,　CuO　nano　labels　were　dissolved　into　Cu2+　ions　under　acidic　condition　to　decrease　the　photocurrent　of　Z-scheme　WO3-Au-CdS　thanks　to　the　formation　of　exciton　trapping　center　of　CuxS　(x　=　1,2)　on　the　surface.　Under　optimum　conditions,　Z-scheme　PEC　immunoassay　exhibited　good　photocurrents　toward　target　PSA　within　a　linear　range　of　0.01-50　ng　mL(-1)　at　a　limit　of　detection　of　1.8　pg　mL(-1).　Moreover,　the　Z-scheme　PEC　immunoassay　had　high　selectivity　and　accuracy.　Importantly,　this　method　provides　a　new　horizon　for　detection　of　disease-related　biomarkers　with　high　sensitivity.