Strong　ionic　character　endows　all-inorganic　perovskite　nanocrystals　(NCs)　with　particular　optoelectronic　features　when　interacting　with　common　polar　solvents,　such　as　water.　However,　the　interaction　mechanism　of　water　affecting　perovskite　NCs　is　still　lack　of　in-depth　understanding.　This　study　systematically　explores　the　roles　of　water　on　CsPbBr3　nanocrystals　(CNCs)　by　finely　controlling　the　polymer　coating　degree　of　polydimethylsiloxane-based　polyurea　(PDMS-PUa).　Through　this　coating,　the　effect　of　water　on　CNCs　is　found　to　experience　from　“fluorescence　quenching”　owing　to　irreversible　crystal　decomposition　towards　“forward　fluorescence　reversibility”　by　crystal　destruction　and　recrystallization.　With　gradually　enhanced　coating,　a　phenomenon　of　“reverse　fluorescence　reversibility”　is　further　observed　in　that　water　begins　to　passivate　the　CNCs’　defect　states.　Finally,　“fluorescent　balance”　can　be　achieved　with　a　thick　enough　coating,　where　water　can　hardly　contact　with　the　CNCs.　Inspired　by　the　fluorescence　reversible　mechanism　discovered,　a　new　wearable　intelligent　sensing　skin　is　demonstrated　by　using　the　CsPbBr3/PDMS-PUa　composite　as　raw　material.　Both　water　contact　and　humidity　change　can　be　perceived　through　photoluminescence　(PL)　intensity,　corresponding　to　stimuli-responsive　sensory　nerves　of　human　skin.　It　is　expected　that　these　findings　will　shed　some　new　lights　on　perovskite　NCs.　[Figure　not　available:　see　fulltext.].　©　2022,　Tsinghua　University　Press.