In　this　work,　a　novel　polymethyl　methacrylate-coated　MAPbBr(3)　nanocrystalline　(MAPbBr(3)@PMMA,　MA=　methylammonium)　electrospinning　film　was　synthesized　by　in　situ　growth　method,　and　NH3　sensor　was　constructed　based　on　the　fluorescence　significant　quenching　of　the　MAPbBr(3)@PMMA　electrospinning　film　after　the　addition　of　NH3　gas.　The　morphology　and　structure　of　MAPbBr(3)@　PMMA　fiber　were　characterized　by　scanning　electron　microscopy,　transmission　electron　microscopy,　powder　X-ray　diffraction,　and　infrared　spectroscopy,　and　its　optical　properties　were　characterized　by　UV-Vis　and　fluorescence　spectroscopy.　The　results　showed　that　the　prepared　NH3　sensor　showed　a　good　linear　relationship　(r=0.995　9)　to　NH3　gas　concentration　in　a　range　of　8-90　mg　center　dot　L-1,　low　detection　limit　(3　mg　center　dot　L-1),　and　high　reproducibility　and　selectivity.　Finally,　the　standard　recovery　and　the　relative　standard　deviation　(RSD)　for　NH3　of　actual　sample　gas　were　92.2%-102.1%　and　1.8%-3.2%,　respectively.