The　intrinsic　instability　of　halide　perovskites　toward　to　external　stimulus,　has　created　a　competitive　advantage　for　designing　stimuli-responsive　materials.　However,　the　external　environment　tuning　reversibly　fluorescence　emission　of　perovskite　system　is　still　limited.　In　this　work,　humidity　is　verified　to　act　as　a　new　option　to　modulate　the　emission　properties　of　mixed-halide　perovskite.　The　perovskite　nanocrystals　(PNCs)　photoirradiated　in　dichloromethane　are　easily　and　stably　redispersed　in　water,　and　emit　bright　fluorescence　which　is　quite　different　from　the　original.　Moreover,　the　perovskites　confined　on　glass　slide　can　reversibly　switch　their　fluorescence　between　blue　and　green　colors　under　moisture.　It　is　demonstrated　that　the　factors　of　different　solubilities　of　CsCl　and　CsBr　in　water,　the　structural　transformation　of　perovskites　and　the　confine　of　glass　matrix　play　key　roles　in　the　reversible　transformation.　Finally,　the　combination　of　hydrochromic　CsPb(BrxCly)(3)　and　water-resistant　CsPb(BrxCly)(3)-polymethyl　methacrylate　have　been　applied　in　advanced　anti-counterfeiting,　which　greatly　improves　the　information　security.　This　work　not　only　give　an　insight　into　the　effects　of　humidity　on　fluorescence　and　structures　of　PNCs,　but　also　offer　a　new　class　of　hydrochromic　PNCs　materials　based　on　reversible　emission　transformation　for　potential　application　in　sensors,　anti-counterfeiting　and　information　encryption.