In　recent　years,　copper-based　halide　scintillators　have　attracted　tremendous　attention　due　to　their　excellent　luminescent　properties　and　low　manufacturing　costs.　Herein,　a　high-performance　and　low-cost　Cs5Cu3Cl6I2　scintillator　is　prepared　by　simple　mechanical　grinding.　The　mixed-halide　Cs5Cu3Cl6I2　phosphor　exhibits　a　blue　emission　centered　at　475　nm　with　a　large　stokes　shift,　originating　from　the　self-trapped　exciton　emission　of　Cu　sites.　The　photoluminescence　quantum　yield　(PLQY)　of　Cs5Cu3Cl6I2　can　be　increased　to　88.4%　from　20.4%　by　the　efficient　suppression　of　the　anion　vacancy　defects.　In　addition,　the　Cs5Cu3Cl6I2　scintillator　shows　a　high　steady-state　X-ray　to　light　conversion　efficiency　of　about　57000　photons/MeV,　good　X-ray　linear　response,　and　low　detection　limit　of　71.9　nGyair/s.　The　X-ray　imaging　results　based　on　theCs(5)Cu(3)Cl(6)I(2)　scintillator　screen　display　a　high　spatial　resolution　of　9.0　line-pairs　per　millimeter　(lp/mm).　Furthermore,　Cs5Cu3Cl6I2　exhibits　good　radia-tion　stability　under　a　total　dose　of　113.58　Gyair.　Overall,　the　Cs5Cu3Cl6I2　scintillator　prepared　by　mechanical　grinding　method　has　the　advantages　of　low　cost,　high　efficiency,　and　good　radiation　resistance,　suggesting　its　huge　potential　in　X-ray　detection　and　imaging.