Photoelectrochemical　(PEC)　sensor　realizes　high　sensitivity　detection　of　biomolecules　and　chemical　substances　through　the　combination　of　photoelectric　conversion　and　chemical　reaction,　which　has　important　significance　in　biomedicine　and　environmental　monitoring.　In　this　work,　we　designed　a　flexible　PEC　sensor　based　on　In2O3-CdS　hierarchical　heterojunction　for　detecting　carcinoembryonic　antigen　(CEA)　in　human　serum.　In2O3-CdS　hierarchical　heterojunction　exhibited　outstanding　photoelectrochemical　performance,　which　lays　the　foundation　for　a　highly　sensitive　detection　process.　The　electron　transfer　process　was　impeded　as　a　result　of　the　antigen　being　recognized　and　captured　by　the　specific　antibody　on　the　electrode　surface,　leading　to　the　decline　of　the　photocurrent　signal.　Based　on　this　principle,　the　PEC　sensor　exhibited　a　good　linear　relationship　range　from　0.002　ng　mL-1　to　20　ng　mL-1　under　the　most　suitable　conditions.　In　addition,　this　PEC　sensor　showed　better　stability　and　reproducibility　in　real　samples　compared　to　the　commercially　available　ELISA　kit.　This　work　provided　a　reliable　method　for　early　cancer　screening　and　diagnosis,　which　exhibited　great　significance　and　broad　prospect　for　improving　cancer　treatment　effect　and　survival　rate.