Metal　halide　perovskites　are　considered　as　a　prospective　candidate　as　optical　gain　media　for　stimulated　emission,　and　the　advancement　of　amplified　spontaneous　emission　(ASE)　of　perovskite　materials　is　gradually　becoming　the　key　to　realize　the　commercialization　of　perovskite　lasers.　Nonetheless,　the　ASE　of　solution-processed　polycrystalline　perovskite　films　still　experiences　a　high　threshold　and　poor　optical　stability　due　to　their　high　defect　density　and　poor　crystalline　quality.　In　this　scenario,　a　noticeably　ameliorated　ASE　performance　with　decreased　threshold　and　greater　photo-stability　is　demonstrated　in　solution-processed　(FAPbI3)0.85(MAPbBr3)0.15　polycrystalline　perovskite　films　by　introducing　a　neoteric　4′-Aminoacetophenone　hydrochloride　(APCl)　additive　with　cost-effective　fabrication.　The　ASE　threshold　of　the　APCl-embedded　perovskite　films　is　prominently　curtailed　from　12.8　to　5.3　µJ cm−2,　with　an　augmented　optical　gain,　ASE　output　intensity,　and　optical　durability.　The　ameliorated　ASE　performance　can　be　credited　to　multifunctional　effects　of　the　APCl　additive　in　the　perovskite　films,　presenting　a　low　defect　density,　an　unambiguously　elevated　photoluminescence,　a　prolonged　decay　lifetime　and　thus　enabling　the　easily　achieved　population　inversion　caused　by　the　attenuated　nonradiative　carrier　recombination　in　the　optical　gain　media.　These　findings　provide　a　significant　foundation　and　pave　the　way　for　realizing　the　electrically　excited　lasing　based　on　the　perovskite　materials.　©　2024　Wiley-VCH　GmbH.