HighlightsImine groups in covalent organic framework (COF) films act as dual-active sites for humidity sensing, inducing an intrinsic enhanced mechanism of reversible protonated tautomerism via water molecule-induced hydrogen bonding.Thecis-ketoimine reciprocal isomerization induces a stretching vibration effect for the ordered conjugated conductive frame of COF films, realizing fast response, wide range, and high sensitivity characteristics for humidity detection.Resistance changes of COF film-based sensors keep a strong linear relationship with low-range relative humidity, reflecting the quantitative sensing mechanism at the molecular level.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01107-4.