Lead　halide　perovskites　have　garnered　significant　attention　in　the　field　of　photoelectrochemistry　due　to　their　outstanding　optical　properties.　Nevertheless,　the　pronounced　susceptibility　of　perovskite　to　water　poses　a　major　limitation　to　its　practical　applications.　A　signal-on　photoelectrochemical　(PEC)　sensor　was　constructed　in　this　work　using　water-resistant　perovskite　nanocrystals　for　the　detection　of　hydrogen　sulfide.　Specially,　the　electrode　surface　was　modified　with　composite　nanomaterials　(CsPbBr3　@PEG-PCL).　In　the　presence　of　H2S,　efficient　heterojunctions　were　formed　through　the　in-situ　generation　of　PbS　on　CsPbBr3　@PEG-PCL,　thereby　enhancing　the　photocurrent　signal.　The　potential　mechanism　behind　this　signal　enhancement　was　extensively　discussed.　The　designed　sensor　exhibited　a　linear　relationship　with　the　concentration　of　H2S　ranging　from　0.02　to　120　mu　M,　with　a　detection　limit　of　6.67　nM.　This　work　opens　up　new　possibilities　for　utilizing　halide　perovskites　in　the　field　of　sensing,　with　promising　applications　in　areas　such　as　food　safety,　environmental　monitoring,　and　biomedical　analysis.