Moisture　penetration　is　one　of　the　main　reasons　for　failure　of　transformer　bushings,　so　an　on-line　monitoring　method　for　transformer　bushings　with　moisture　based　on　air　humidity　perception　in　conservator　is　proposed　in　this　paper.　Firstly,　implementation　principles　and　key　issues　were　expounded.　Then,　a　simulator　of　a　transformer　bushing　with　moisture　was　designed　and　made.　Finally,　the　migration　characteristics　of　water　between　oil　and　air,　the　influence　rule　of　the　interface　radius　on　response　characteristics　of　monitoring　device,　and　the　sensitivity　and　error　characteristics　of　humidity　indicator　cards,　were　studied　experimentally.　The　experimental　results　show　that　the　monitoring　device　can　response　rapidly　once　liquid　water　enters　into　the　bushing　and　touches　with　the　air,　however,　the　water　balance　between　damp　transformer　oil　and　dry　air　takes　60~80　hours.　The　larger　the　interface　radius,　the　shorter　the　response　time　of　monitoring　device,　and　the　absolute　humidity　in　the　monitoring　device　rises　the　most　quickly　when　the　interface　radius　is　6　mm.　The　indication　error　of　humidity　indicator　cards　increases　with　the　temperature.　Finally,　an　adjustment　method　for　the　humidity　indicator　card　by　considering　the　influence　of　temperature　has　been　proposed　to　realize　the　color　changing　alarm　for　moisture　in　the　transformer　bushing　under　different　operation　temperatures.　©　2020,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.