Inorganic　metal　halide　perovskite　quantum　dots　(PQDs)　have　recently　emerged　as　promising　candidates　for　color　conversion　materials　in　Micro-LED　displays,　due　to　their　outstanding　color　purity,　high　absorption　coefficient,　tunable　emission　wavelength.　However　the　inferior　stability　and　undesirable　photoluminescence　quantum　yield　(PLQY)　restrict　their　particle　applications.　Herein,　CsPbX3/PMMA　(X　=　Br,　I)　composites　with　improved　stability　and　optical　performance　were　successfully　prepared　by　a　general　and　mild　in-situ　polymerization　strategy.　The　ester　carbonyl　(C--O)　group　in　MMA　formed　complexes　with　Pb2+,　leading　to　the　in-situ　thermal　polymerization　of　polymethyl　methacrylate　(PMMA)　under　the　action　of　the　initiator.　The　multifunctional　PMMA　can　efficiently　passivate　halogen　vacancies　while　acting　as　a　barrier　against　the　degradation　caused　by　heat,　water,　and　oxygen.　As　a　result,　the　PLQYs　and　stability　of　PMMA-coated　CsPbX3　PQDs　have　been　significantly　improved.　When　implementing　CsPbX3/PMMA/PDMS　composites　as　color　conversion　layers　in　Micro-LEDs,　they　achieve　an　impressive　color　gamut　of　127.23%　with　excellent　stability.　We　believe　our　work　will　stimulate　the　exploration　of　perovskite/polymer　composites　for　industrial　Micro-LED　applications.