A　photoelectrochemical　(PEC)　sensing　system　for　H2O2　detection　had　been　proposed　based　on　parallel　catalytic　method　in　the　presence　of　a　ferrocene　derivative.　3,3-bis(1-ferrocene　methyleneimidazole-3-)　boron　dihydrodicyanamide　([Fcmim]　[N(CN)(2)])　was　synthesized　and　immobilized　on　the　surface　of　a　GaN　photoanode　by　the　Nafion　(R)　film.　A　circulating　H2O2-O-2-H2O2　system　was　constructed　using　[Fcmim][N(CN)(2)]　as　bifunctional　catalyst.　In　the　cyclic　process,　H2O2　is　catalyzed　by　[Fcmim]　[N(CN)(2)]　to　produce　O-2,　which　is　then　reduced　to　H2O2　by　photogenerated　electrons　of　GaN.　The　reduction　process　of　O-2　is　also　catalyzed　by　the　same　ferrocene　catalyst.　The　regenerated　H2O2　continues　to　be　decomposed,　causing　O-2　and　H2O2　to　fall　into　a　photoelectrochemical　cycle　of　H2O2-O-2-H2O2.　The　decrease　of　the　photocurrent　by　O-2　was　markedly　amplified　because　the　H2O2　and　O-2　were　periodically　regenerated.　On　the　other　hand,　the　diffusion　rate　of　dissolved　O-2　through　the　Nafion　(R)　film　is　lower　than　the　photoelectrochemical　reduction　rate　of　O-2　on　the　GaN　photoanode,　thus　the　interference　of　dissolved　O-2　in　the　solvent　could　be　eliminated　during　repeated　on/off　cycles　of　illumination.　In　the　range　of　4.00　nM　-　0.720　mu　M　and　the　limit　of　detection　was　1.23　nM　(3　S/N),　PEC　signal　is　linearly　correlated　with　the　logarithm　of　H2O2　concentration　under　optimized　conditions.　This　method　has　a　wide　application　prospect　in　environmental　analysis　and　food　safety　analysis.　For　example,　bilirubin　can　be　detected　using　Nafion　(R)　in　combination　with　bilirubin　oxidase　and　[Fcmim]　[N(CN)(2)].