Metal　halide　perovskite　nanocrystals　are　known　for　their　impressive　photoelectric　properties.　However,　their　inferior　stability　and　tendency　to　agglomerate　in　solution　jeopardized　perovskite　nanocrystal　application.　To　mitigate　this　issue,　a　method　is　developed　for　filling　perovskite　precursor　into　mesoporous　silica　(MS)　films　with　subsequent　thermal　sintering　to　form　nanocrystals　in　a　ceramic　matrix.　The　perovskite　precursor　vapor　state　was　utilized　instead　of　a　liquid　state　or　solid　one,　allowing　maximum　diffusion　ratio　into　vertically　aligned　numerous　ultrasmall　nanopores　(approximate　to　4　nm)　in　MS　during　the　thermal　sintering　process.　Then,　the　annealing　step　enables　the　pore　to　collapse　to　encapsulate　as-grown　perovskite　nanocrystal　simultaneously.　This　collapse　of　the　mesoporous　structure　ensures　that　the　perovskite　can　be　sealed　to　mitigate　the　degradation　from　moisture　and　oxygen.　As　a　result,　a　less　discernible　photoluminescence　degradation　was　observed　when　the　perovskite-MS　thin　film　is　soaked　in　water.　Furthermore,　these　films　demonstrate　distinguished　thermal　stability,　benefiting　from　their　unique　structure　of　inorganic　silica　anchored　onto　perovskite　surfaces.　An　amplified　spontaneous　emission　signal　is　monitored　in　the　vertically　aligned　MS-coated　perovskite　film.　The　encapsulated　strategy　provides　ultrastable　and　highly　emissive　perovskite　film　that　fits　the　technological　requirements　of　potential　laser　application.