Low　dimensional　metal　halide　perovskites　(MHPs)　have　a　soft　lattice,　leading　to　strong　exciton　phonon　coupling　and　exciton　localization.　Microstructural　stiffness　engineering　is　an　effective　tool　for　modulating　the　mechanical　and　electrical　properties　of　materials,　but　its　complex　effects　on　the　luminescence　of　low　dimensional　MHPs　remain　lacking.　Here,　we　report　microstructural　stiffness　engineering　of　low　dimensional　MHPs　by　halogen　replacement　in　Ag-X　bonds　and　[AgX4]3-　(X　=　Br,　Cl)　units　to　increase　the　Young＇s　modulus　from　15.6　to　18.3　GPa,　resulting　in　a　10-fold　enhancement　of　X-ray　excited　luminescence　(XEL)　intensity　and　a　16-fold　enhancement　of　photoluminescence　quantum　yield　(PLQY),　from　2.8%　to　44.3%.　Spectroscopic　analysis　reveals　that　high　stiffness　in　Rb2AgCl3　facilitates　the　radiative　pathway　of　defect-bound　excitons　and　efficiently　decreases　the　non-radiative　transitions.　The　projected　crystal　orbital　Hamilton　population　shows　that　the　shorter　Ag-Cl　bonds　impart　Rb2AgCl3　with　superior　anti-deformation　ability　upon　photoexcitation,　leading　to　enhanced　radiation　resistance　performance.　A　scintillation　screen　based　on　Rb2AgCl3@PDMS　achieves　zero　self-absorption,　an　ultra-low　detection　limit　of　44.7　nGyair　s-1,　and　a　high　resolution　of　20　lp　mm-1,　outperforming　most　reported　X-ray　detectors.　This　work　sheds　light　on　stiffness　engineering　for　the　rational　design　of　efficient　emitters.　We　report　microstructural　stiffness　engineering　of　metal　halide　perovskites,　resulting　in　an　increase　in　the　Young＇s　modulus　from　15.6　to　18.3　GPa.　This　leads　to　a　10-fold　and　16-fold　enhancement　in　the　luminescence　intensity　and　quantum　yield.