We　report　a　Mn2+-activated　all-inorganic　2D　layered　Ruddlesden-Popper　(RP)　perovskite　Cs2CdCl4　single　crystal　as　a　highly　efficient　and　stable　X-ray　scintillator.　The　Cs2CdCl4:10%　Mn　achieves　a　bright　orange-red　emission　with　a　photoluminescence　quantum　yield　up　to　90.47%,　good　environmental　stability,　and　decent　thermal　quenching　resistance.　As　a　scintillator,　Cs2CdCl4:10%　Mn　shows　strong　X-ray　absorption,　ultrahigh　light　yield　up　to　88138　photons/MeV,　and　low　detection　limit　of　31.04　nGy(air)/s.　A　15　x　15　cm　flexible　scintillation　screen　is　prepared　by　mixing　poly(dimethylsiloxane)　(PDMS)　with　Cs2CdCl4:Mn　powder,　which　demonstrates　superior　X-ray　imaging　performance　with　a　high　spatial　resolution　of　16.1　lp　mm(-1)　at　a　modulation　transfer　function　(MTF)　=　0.2.　Importantly,　due　to　the　ultrahigh　X-ray　sensitivity,　the　flexible　scintillator　screen　achieved　clear　X-ray　imaging　at　an　extremely　low　dose　of　16　mu　Gy(air)/s.　This　successful　exploitation　of　the　2D　high　light　yield　perovskite　scintillator　in　flexible　low-dose　X-ray　imaging　would　provide　new　insight　into　high-sensitivity　X-ray　detection.