The　effective　removal　of　the　low-concentration　formaldehyde　(HCHO)　in　the　indoor　environment　is　a　critical　issue　affecting　the　quality　of　people＇s　daily　lives.　In　this　study,　heterojunction　catalysts　composed　of　manganese　dioxide　(MnO2)　and　cesium　tin　iodine　(CsSnI3)　nanocrystals　were　first　synthesized　and　successfully　used　for　photocatalytic　HCHO　degradation.　After　the　full　band　light　irradiation　(150　mW/cm(2))　for　3　h,　the　concentration　of　HCHO　decreased　from　7　ppm　to　a　minimum　of　0.03　ppm　at　room　temperature　(25　degrees　C,　25　%　RH,　degradation　efficiency　reaches　up　to　99.6　%).　Subsequent　analysis　using　electron　paramagnetic　resonance　(EPR)　and　transmission　electron　microscopy　(TEM)　revealed　that　the　MnO2-CsSnI3　heterojunction　photocatalyst　not　only　offers　a　Z-scheme　charge-transfer　pathway　but　also　promotes　the　generation　of　a　large　number　of　center　dot　O-2(-)　and　center　dot　OH.　Compared　to　the　single-phase　material,　the　concentration　of　center　dot　O-2(-)　and　center　dot　OH　has　increased　by　1.5　times.　This　MnO2-based　Z-scheme　heterojunction　photocatalyst　provides　a　novel　strategy　for　the　degradation　of　low-concentration　HCHO　in　practical　indoor　environments.