Deployable/retractable　damped　cantilever　beams　are　a　class　of　time-varying　parametric　structures　which　have　attracted　considerable　research　interest　due　to　their　many　potential　applications　in　the　intelligent　robot　field　and　aerospace.　In　the　present　work,　the　dynamic　characteristics　of　a　deployable/retractable　damped　cantilever　beam　are　investigated　experimentally　and　theoretically.　The　time-varying　damping,　as　a　function　of　the　beam　length,　is　obtained　by　both　the　enveloped　fitting　method　and　the　period　decrement　method.　Furthermore,　the　governing　equation　of　the　deployable/retractable　damped　cantilever　beam　is　derived　by　introducing　the　time-varying　damping　parameter,　and　the　corresponding　closed-form　solution　and　vibration　principles　are　investigated　based　on　the　averaged　method.　The　theoretical　predictions　for　transient　dynamic　responses　are　in　good　agreement　with　the　experimental　results.　The　dynamic　mechanism　analysis　on　time-varying　damping　offers　flexible　technology　in　mechanical　and　aerospace　fields.