Sluggish　charge　transfer　and　rapid　electron-hole　recombination　severely　limit　the　analytical　performance　of　photoelectrochemical　(PEC)　immunoassays.　This　work　presented　a　PEC　immunosensing　strategy　that　employed　a　target-induced　enzyme-catalyzed　reaction　to　in-situ　generate　oxygen　vacancy　(Ov)　for　amplifying　the　photocurrent　detection　of　carcinoembryonic　antigen　(CEA).　Concretely,　ascorbic　acid-2-phosphate　(AAP)　was　catalyzed　to　produce　ascorbic　acid　(AA)　by　alkaline　phosphatase　(ALP)　in　the　presence　of　CEA.　The　generated　AA　could　serve　as　a　reducing　agent　to　introduce　oxygen　vacancy　(Ov)　into　the　etching　tungsten　trioxide　(E-WO3)　photoanode,　resulting　in　an　Ov-enriched　E-WO3　(E-WO3-Ov)　photoanode.　The　formation　of　Ov　allowed　efficient　introduction　of　defect　levels　into　the　energy　band　structure　of　E-WO3-Ov　photoanode,　resulting　in　high　charge　transfer　and　electron-hole　separation　efficiency　for　photocurrent　amplification.　Later,　it　was　applied　to　fabricate　a　PEC　immunosensor,　thus　enabling　a　wide　linear　range　from　0.02　to　80　ng/mL　and　a　low　detection　limit　of　12.9　pg/mL.　Overall,　this　work　presented　a　promising　sensing　strategy　for　PEC　immunosensors,　expanding　the　scope　of　potential　applications　in　bioassays　and　clinical　diagnostics.